Module 4 - Forensic Ballistics

Module 4  -  Forensic Ballistics

Forensic ballistics involves the scientific analysis and interpretation of evidence and phenomena related to the illegal use of firearms. For more than a century, the collection of evidence related to the use of firearms in the commission of criminal offences has been a standard investigative tool. Information critical to the successful investigation of firearm-related crimes is obtained from various sources, including matching a bullet to the gun from which it was fired, analyzing traces of gun residue found on a suspect, and tracing shell casings left at a crime scene to a particular firearm.

• Lesson 1 of this module outlines the basic types of firearms and the unique velocity, kinetic energy, and trajectory capabilities of each type. This lesson also outlines the main components of bullet cartridges and firearms.
• Lesson 2 examines the distinct properties within gun barrels and the ways these properties help law enforcement in criminal investigations involving firearms. This lesson also addresses the concept of ballistic fingerprinting.
• Lesson 3 describes five types of testing for gunpowder residue.
• Lesson 4 explores one historical crime case and one fictional crime, both relating to forensic ballistics.

Module Learner Objectives

By the end of Module 4, you should be able to…

• understand that forensic ballistics involves the scientific analysis of evidence from crime scenes in which a firearm was used (such as firearms, bullets, bullet holes, bullet trajectories, cartridges cases, and gunshot wounds)
• appreciate that forensic ballistics involves internal ballistics, external ballistics, and terminal ballistics
• outline the major components of a handgun cartridge, a rifle cartridge, and a shotgun shell
• describe how the structure, function, velocity, kinetic energy, and trajectory of the three main types of firearms (handguns, rifles, and shotguns) differ
• graph and analyze data to compare the average velocity, kinetic energy, and trajectory of handgun, rifle, and shotgun rounds
• recognize that gun barrels have unique lands and grooves and that these markings leave unique marks or ballistic fingerprints upon fired casings
• discuss the possible value of a comprehensive national or global ballistic fingerprint data bank and propose the positive and negative implications of having such a data bank
• understand that forensic ballistic experts use various gunpowder and/or primer residue chemical test techniques to determine if a suspect has fired a gun
• describe how forensic experts test for gunpowder residue and primer residue using various scientific techniques and technologies (such as Paraffin Test, Modified Greiss Test, Sodium Rhodizonate Test, Harrison-Gilroy Test, Neutron Activation Analysis and/or Flameless Atomic Absorption System, and X-ray analysis using a scanning electron microscope)
• discuss one historical crime case (such as Washington sniper shootings and John F. Kennedy assassination) and one fictional crime case that involve forensic ballistics

Glossary

ammunition: projectiles, such as bullets, together with their fuses and primers that can be fired from guns or otherwise propelled

bipod: a stand having two legs, as for the support of an instrument or a weapon

calibre: the diameter of the bore of a firearm, traditionally shown in hundredths or thousandths of an inch, but may be in millimetres

carbine: a lightweight rifle with a short barrel

cavitation: the formation of an empty space within a solid object or body

concealment: hiding or kept from being seen, found, or discovered

combustion: a chemical change accompanied by the production of heat and light

corrodes: the gradual destruction of a metal or alloy, especially oxidizing or chemical action (rusting)

firing pin: the part of the bolt or breech of a firearm that strikes the primer and detonates the charge of a projectile (bullet)

gun barrel: the tube through which a bullet travels when a gun is fired

kinetic energy: the energy possessed by a body because of its motion

muzzle: the forward, discharging end of the barrel of a firearm

pellets: small, metal balls found within certain types of shotgun cartridges

polyatomic ions: an ion of two or three atoms that has a charge and acts as a single unit (for example, hydroxide ion = oh-)

projectile: a fired or propelled object, such as a bullet, that with no capacity for self-propulsion

propellant: something that propels or provides thrust; especially gunpowder

reagent: a substance used in a chemical reaction to detect, measure, examine, or produce other substances

ricochet: to rebound or bounce at least once from a surface

semi-automatic: a firearm that requires a squeeze of the trigger for each shot, but it ejects the cartridge casing and loads the next round of ammunition automatically

Tarot cards: a set of cards to represent virtues, vices, death, and fortune, etc.; used by fortune-tellers

trajectory: the path through space of a projectile or other moving body

velocity: the speed and direction of a body in motion

Revolver

Shotgun

Pistol

Rifle

 

 

 

 

 

 

 

 

 

 

 

The first forensic firearm identification occurred in England in 1835 when the distinctive markings on a bullet taken from a victim were matched with a bullet mould belonging to the suspect. When confronted with this evidence, the suspect confessed to the crime.

Internal, External, and Terminal Ballistics

Ballistics is a science that deals with the motion, behaviour, and effects of projectiles (such as bullets, rockets, and missiles). Forensic ballistics involves the science of analyzing the motion, behaviour, and effects of a bullet fired from a gun. The study of forensic ballistics has three sub-categories: internal ballistics, external ballistics, and terminal ballistics.

1.   Internal ballistics is the study of the evidence produced inside a firearm when a bullet or round is fired. This includes the study of firearm mechanisms, gun barrel manufacturing techniques, factors influencing the internal gas pressure within a particular firearm, and firearm recoil. The most common types of internal ballistics involve:

• examining the working mechanisms of firearms to determine the cause of accidental discharges.
• examining homemade devices (sometimes called zip guns) to determine whether they are capable of discharging ammunition effectively.
• comparing fired bullets and cartridge cases to determine whether a particular firearm was used.

2.  External ballistics is the study of the bullet's flight from the moment it leaves the muzzle of the firearm's barrel until it strikes a target. The two most common types of external ballistics forensic examinations involve

• calculating and reconstructing of bullet trajectories
• determining the maximum range of a given bullet

3.  Terminal ballistics is the study of a bullet’s effect on the target or the counter effect of the target on the bullet. Wound ballistics is a form of terminal ballistics in which the target is a human or an animal. Common types of terminal ballistics forensic examinations include:

• determining the distance between firing point and target
• establishing whether a particular bullet caused the wound in question
• determining the calibre and type of bullet that caused damage or, in the case of a human victim, a gunshot wound
• identifying the entry and exit points of a bullet in a static target or human body
• examining ricochet possibilities of targets and fired bullets

The term revolver is derived from the fact that individual bullet cartridges (bullets or rounds as they are commonly known) are loaded into a cylinder that revolves slightly with each pull of the trigger. The cylinder advances so that the next bullet is brought into line with the opening of the barrel.

As the firing pin strikes the bullet’s primer (located at the centre of the base of the cartridge), the gunpowder in the cartridge casing explodes, forcing the bullet out of the cylinder, into the opening of the barrel, down the length of the barrel, and out the muzzle.

A muzzle blast can be quite substantial in revolvers, especially where the cylinder lines up with the opening of the barrel. A revolver typically holds six cartridges in one of various calibres such as .22, .38, .357, and .44 (spoken as twenty-two, thirty-eight, three fifty-seven, and forty-four). The calibre of a firearm refers to the diameter of the bullet, usually measured in tenths of an inch. Therefore, a .38 calibre revolver fires a bullet that is 0.38 inch in diameter. Rather than refer to this diameter in metric units, the firearms industry has retained these commonly understood terms.

The ballistic property of revolver ammunition varies by calibre. Typically, .22 and .38 calibre ammunition have low muzzle velocities and limited amounts of kinetic energy. The structure and design of revolvers, specifically because of the use of a cylinder, result in significant loss of kinetic energy and muzzle velocity due to the escape of gases around the cylinder and barrel opening when the gun is fired.

Revolvers remain popular among collectors and people who like to target shoot as a hobby. Law enforcement agencies have generally discontinued their use of revolvers because of low ammunition capacity, lengthy reloading time, and inadequate muzzle velocity.

The Pistol

A pistol is characterized by semi-automatic features in which a slide sits on top of the frame. Bullet cartridges are loaded into a holding device called a magazine that is inserted into the handle of the pistol. The barrel sits inside the slide. Each pull of the trigger and discharge of a cartridge produces a recoil force that moves the slide back drawing a new bullet into the opening of the barrel. The slide then returns to its forward position, locking the bullet into the barrel. When the trigger is pulled again, the process repeats. Pistol bullet velocity can be considerably higher than a revolver’s velocity because the hot gases emerging from the bullet casing are contained within the barrel of the pistol, thereby increasing the pressure acting against the bullet as it moves down the barrel and out the muzzle.

The unique design of semi-automatic pistols allows for faster reloading times, higher firing rates, and higher magazine capacities (typically 10 to 16 bullets per magazine). The trigger can be pulled in rapid succession while keeping the pistol on target. For example, a person using the .40 Glock pistol is able to fire fifteen rounds of ammunition continuously before loading a new magazine.

Pistol ammunition varies in calibre, with 9 mm, .40, and .45 being the most common. Law enforcement agencies across North America typically use 9 mm or .40 calibre pistols although .45-calibre pistols are sometimes used.

While occasionally prone to jamming if not properly maintained, automatic weapons have increased among criminals in recent decades. Therefore, law enforcement agencies have adopted semi-automatic pistols because of their large magazine capacity. In addition, police are now using hollow point bullets. Recent trends include the use of semi-automatic rifles (carbines) by patrol officers in response to the increased firepower of some criminals. The public became aware of this increased firepower because of such high profile incidents as the 1994 North Hollywood shootout in Los Angeles.

Semi automatic pistol Cartridges

Bolt-action rifles are reliable and easy to maintain. These rifles vary widely in calibre and purpose. They are characterized by a handle (bolt) on the side that allows the user to extract a spent cartridge and place a new one into the barrel from the magazine by sliding the bolt back and then forward.

Bolt-action rifles typically hold up to five cartridges and must be reloaded after each round is fired. Telescopic sights help bring targets into focus over long distances. Depending on its calibre, the use of a telescope mounted along the barrel above the action of the rifle increases the effective range of a bolt-action rifle to between 200 metres and 1000 metres (1 kilometre).

Because of the longer shell casings, bolt-action rifle bullets possess extremely high muzzle velocities and kinetic energies. For example, while a standard .40 calibre pistol round commonly used by police agencies has a muzzle velocity of 305 metres/second and 542 Joules of kinetic energy, a .308 round from a police sniper’s bolt-action rifle has a muzzle velocity of over 792 m/s and almost 3660 J of kinetic energy! In other words, a rifle bullet is smaller in diameter, travels faster, and has much more kinetic energy than a bullet fired by either a revolver or a pistol.

Just as muzzle velocity, kinetic energy, and trajectory vary with revolver and pistol ammunition, they also vary widely depending on the calibre of the rifle bullet. However, the trajectory of rifle bullets can in some cases be much flatter than that of handgun ammunition. For example, a handgun round fired parallel to the ground might fall into the dirt after it has travelled the length of two football fields. A rifle bullet used in big game rifles might travel over 3 kilometres before doing so.

The Automatic Rifle

Typically referred to as assault rifles, an automatic rifle is characterized by its ability to fire a continuous stream of bullets with each pull of the trigger. The rifle pictured above is a version of the standard weapon used by the US military and increasingly by police agencies across North America.

Assault rifles are highly accurate up to approximately 200 metres. They are designed for combat scenarios in which a large number of bullets are directed at a target in a brief time. Automatic weapons such as the AR-15 have been modified for law enforcement use and are valued for their accuracy and stopping power.

Automatic weapons, whether machine guns, assault rifles, or submachine guns, are available for various sizes of ammunition, including .223, 9 mm, and 7.62 mm. Most of these ammunition rounds have relatively flat trajectories. This means that a bullet can travel a great distance without falling into the ground. For example, the .223 round commonly used in the AR-15 rifle might drop only 1 to 2 cm as it travels the length of two football fields. Consequently, automatic weapons are highly accurate under controlled conditions.

Rifle Cartridges

The Shotgun

Shotguns were designed to spray lead pellets over a large area. They are ideal for hunting birds or small animals that move quickly. Shotguns are very popular due to their versatility and durability. The 12-gauge Remington 870 shotgun has been issued in law enforcement agencies for decades.

Shotguns fire shells rather than cartridges from a magazine holding three or four rounds. They can fire a wide variety of shells in various calibres. Birdshot typically consists of a large number of small lead pellets packed within the shell, which sits above a brass casing and primer. Buckshot consists of a smaller number of lead pellets, each of which is larger in diameter than birdshot. Typical buckshot rounds used by police agencies contain approximately nine lead pellets, each the size of a small pea. Its effective range is limited to 20 to 30 metres. Rifle slugs are also used in shotguns, increasing the effective range of a shotgun to approximately 100 metres (the length of a football field). Slugs are lead bullets about the size of a man’s thumb. They have substantial amounts of kinetic energy over short distances. However, they rapidly lose height after approximately 100 metres. Therefore, shotgun slugs are inaccurate past that distance.

To gain a better understanding of the science behind forensics ballistics, one must understand the basic parts of a firearm and the assembly of rifle and pistol cartridges.

The Main Parts of a Firearm Cartridge

Cartridges are often referred to as bullets although this is technically an inaccurate term. A bullet is just one component of the various parts of a cartridge. A cartridge consists of a casing (2) made from brass with a primer (5) at its base (4); the casing is filled with a particular amount of gunpowder (3) on top of which sits a projectile called a bullet (1).

A Handgun Cartridge

The photograph above displays two .357 handgun cartridges. The primer mounted in the base of each bullet is displayed in the upper right photograph. The silver-coloured casing contains a hollow point bullet designed to increase stopping power. The bullet is in the brass-coloured casing is the wadcutter design intended for target practice.

A Rifle Cartridge

Rifle (or long-gun) cartridges utilize the same basic designs as handgun cartridges and can carry the same calibre bullet as a pistol cartridge, but they contain larger amounts of gunpowder in the elongated casings. As a result, muzzle velocities of bullets leaving a rifle barrel are often much higher than the muzzle velocities of handgun rounds.

The mechanics of loading and firing a cartridge are essentially the same in both types of firearms. A cartridge is initially loaded into the cylinder or magazine of the firearm. Then, it is manually loaded into the breech by cocking the weapon. This places the firing pin in a position immediately behind the primer. When the person using the firearm pulls the trigger, the firing pin is released, and it strikes the primer. When the primer is detonated, it ignites the gunpowder in the casing, causing a controlled explosion in which a high-pressure pulse of hot-gas is released to force the bullet out of the casing and down the length of the gun’s barrel. The longer the barrel, the greater the muzzle velocity because the exploding gases have more time to exert pressure on the bullet. As the bullet leaves the muzzle of the gun, a brief flash may be evident followed by smoke and the scent of gunpowder as gases escape. The empty casing usually remains in the cylinder of a revolver or rifle.

With a semi-automatic weapon, the recoil results in the used casing being ejected and a new cartridge chambered. This happens once per trigger pull. Revolvers are structured in a fundamentally different way—each pull of the trigger causes the cylinder to turn slightly. This movement lines up another chamber with the barrel of the gun.

Velocity, Kinetic Energy, and Trajectory of Firearms

Two essential objectives in forensic ballistics involve determining what type of firearm was used in a crime and the position of the suspect using the firearm in relation to the victim. The velocity, kinetic energy, and trajectory of the bullet(s) fired from the suspect’s firearm must be determined to answer these questions. Therefore, understanding these concepts and their relationship to the application of forensic ballistics is important.

Velocity (v) is a measurement of both the speed and direction of a bullet once it leaves the barrel of a firearm. Velocity differs according to cartridge specification and barrel length. The mathematical equation used to determine velocity is distance (d) divided by time (t) or v = d/t. In forensic ballistics, the velocity of a bullet is measured in metres per second (m/s).

Kinetic energy (E_k) is the energy possessed by a bullet after it leaves the barrel of a firearm. The kinetic energy of a bullet is determined by the type of gun and the amount of gunpowder in the bullet cartridge. If the amount of gunpowder in the cartridge is held constant, the amount of kinetic energy produced by the gun is also constant. The speed of the bullet when it exits that gun is determined by the equation E_k=1/2mv² (one-half the mass times the square of the velocity) and so, if you have a lighter bullet being fired from the gun, that bullet will travel more quickly (or have a greater velocity) than a heavier bullet fired by the same gun. In forensic ballistics, the kinetic energy of a bullet is measured in Joules (J).

Trajectory is the flight path (arc) of a bullet after it leaves the barrel of a firearm and travels towards the intended target. The arc of a bullet’s flight path depends upon its muzzle velocity and mass. All bullets have a parabolic trajectory. However, lighter bullets possessing higher muzzle velocity tend to have a flatter trajectory, and heavier bullets with lower muzzle velocity tend to drop more dramatically in a shorter time. The trajectory of a bullet is determined by the effect of gravity on the bullet in relation to the change in its kinetic energy over time. In forensic ballistics, the trajectory of a bullet is measured by the loss of vertical distance per metre travelled.

Graphing Activity:

Velocity, Kinetic Energy, and Trajectory of Ammunition Fired from Various Types of Firearms

Forensic ballistic experts can accurately reconstruct the events that occurred at a crime scene when a firearm is involved because each type of firearm has unique characteristics of velocity, kinetic energy, and trajectory. For example, after the Washington sniper shootings in the fall of 2002, ballistic experts linked the suspect’s firearm to almost all the shootings by examining the bullet fragments found in each victim. The location of each shooting victim enabled forensic experts to determine approximately where each suspect had been hiding when the shot was fired.

In this activity, the creation of three graphs comparing the velocity, kinetic energy, and trajectory of three basic types of firearms (handguns, rifles, and shotguns) will help you see the unique ballistic properties exhibited by each. After you have completed each graph, answer the related questions.

Click Here for graphing question number one.

Click Here for graphing question number two.

Click Here for graphing question number three.

Comparison of the VELOCITY of Ammunition Fired from Various Firearms

Problem: How do the average velocities of handgun, rifle, and shotgun rounds differ?

• Use the data below to plot three lines on one graph.
• Use the x-axis to represent the three distances: 0 m (muzzle), 50 m, and 100 m.
• Use the y-axis to represent bullet velocity (in metres/second).
• Provide a legend for your graph; a title is given.

Click Here for paper to use as a graph.

Related Questions:

Velocity of Ammunition Fired from Various Firearms

1. Which type of firearm shoots bullets with the highest initial velocity?
   Ans.  Rifle / .223 Remington
2. What happens to the velocity of each type of bullet as it moves away from where it was shot?
   Ans.  They all slow down.
3. Which type of ammunition loses speed at the quickest rate?
   Ans.  Shotgun slug

Comparison of the KINETIC ENERGY of Ammunition Fired from Various Firearms

Problem: How do the kinetic energy levels of a handgun, a rifle, and a shotgun differ?

• Use the data below to plot three lines on one graph.
• Use the x-axis to represent the three distances: 0 m (muzzle), 50 m, and 100 m.
• Use the y-axis to represent kinetic energy (in Joules).
• Provide a legend for your graph; a title is given.

Click Here for paper to use as a graph.

Related Questions:

Kinetic Energy of Ammunition Fired from Various Firearms

1. Which firearm projects its bullet with the most kinetic energy? Explain.
   Ans.  Shotgun / .12-gauge slug. This firearm likely causes the most kinetic energy to be generated because the .12 gauge slug contains more gunpowder than the other rounds.
   
2. Why does the kinetic energy of each bullet decline as it moves away from where it was shot?
   Ans.  Kinetic energy is a function of mass and velocity (Ek = 1/2mv2). Therefore, as each bullet moves, its kinetic energy decreases because its velocity decreases (as shown in graph #1).
3. Which type of ammunition loses kinetic energy at the slowest rate?
   Ans.  9 mm Luger / jacketed hollow point

Comparison of the TRAJECTORY of Ammunition Fired from Various Firearms

Problem: How does the trajectory of a projectile differ when fired by a handgun, a rifle, or a shotgun?

• Use the data below to plot three lines on one graph.
• Use the x-axis to represent the three distances: 0 m (muzzle), 50 m, and 100 m.
• Use the y-axis to represent change in height in centimetres.
• Provide a legend for your graph; a title is given.

Click Here for paper to use as a graph.

Related Questions:

Trajectory of Ammunition Fired from Various Firearms

1. Explain which type of firearm ammunition is the most accurate at hitting its target at short range (50 m).
   Ans.  The pistol is the most accurate at hitting its target at short range.  Its bullet falls only 2.1 metres; the rifle and shotgun fall 2.9 m and 3.8 m respectively.
   
2. Explain which type of firearm ammunition is the most accurate at hitting its target at longer ranges.
   Ans.   The rifle (.223 Remington) is the most accurate at hitting its target at long range. Its bullet falls only 14 cm after travelling 200 metres; the pistol and the shotgun rounds each fall 21.9 cm and 31.8 cm respectively.

In any criminal investigation where a firearm has been used, evidence may be analyzed, which includes the weapon, a bullet, a piece of the bullet (fragment), a cartridge casing, bullet holes, the injury caused by the bullet, or even gunpowder residue. All these clues can be used to match a suspect weapon to a crime.

Ballistic Fingerprinting

Ballistic fingerprinting involves the identification of unique markings on bullets and cartridge casings that have been located at crime scenes. By comparing the striations and marks left on a bullet or shell casing recovered at a crime scene to those left on a bullet or shell casing by a gun that has been test fired in a laboratory, police can determine whether that specific firearm was involved.

Land and Groove Impressions

The interior of the barrel in every gun contains unique striations called lands and grooves. The lands are raised ridges, and the grooves are recessed portions between each of the ridges. Known as rifling, these lands and grooves are cut into the barrel during production to increase the accuracy of that firearm. When the gun is discharged, these lands and grooves cause the bullet to spin as it travels the length of the barrel. This stabilizes the bullet during flight. At the same time, the expansion of the fired cartridge and the high pressure propelling the bullet through the barrel press and scrape the bullet against the rifling as it moves toward the muzzle. As a result, the fired bullet has unique microscopic striations left upon its exterior from the lands and grooves. These striations are called land and groove impressions by forensic firearm investigators.

Because rifling is randomly generated during manufacture or due to wear, no two gun barrels leave the same land and groove impressions upon a bullet. This uniqueness enables the identification of bullets as having originated from a particular gun.

To link a bullet to a particular firearm, forensic ballistics experts typically fire a crime scene weapon into a tank of water and then retrieve the test bullet. The test bullet is then compared to the bullet in question using a comparison microscope. If the land and groove impressions match, a photograph is taken for use as evidence in court. However, if a weapon is not left at the crime scene and the crime scene investigators are able to retrieve an intact bullet from the victim or the scene, they can only make assumptions about the type and model of firearm used based on the calibre of the bullet and the wound ballistics. Simply based on the rifling impressions on a particular bullet, it would be impossible for investigators to deduce the type and model of firearm because rifling impressions are unique for every gun not for every type of gun (for example, all .44 magnum pistols will not have similar rifling impressions). The only exception would be if the same gun had been used in a previous crime and both the bullet and the gun had been entered into the ballistic's database.

The microscopic land and groove impressions found on the surface of fired bullets are routinely used to match bullets with a suspects’ weapons. Impressions can be found on cartridge cases as well, and these can be used to match a cartridge case to a specific firearm. Firing pin impressions, extractor marks, ejector marks, chamber marks, and ammunition stamps on the cartridge casing are all features analyzed by forensic firearm experts.

Firing pin impressions are left during the discharge of a firearm. The firing pin creates microscopic features of the indentation left when it strikes the primer of a cartridge.

Extractor and ejector marks are produced when the cartridge case is mechanically extracted from the chamber. Visible fine striations and impressions are left on the rim and head of the casing.

Chamber marks are parallel striations on the cartridge case caused by contact with the walls of the chamber of the firearm.

Ammunition stamps consist of information about the type of ammunition stamped by the manufacturer onto the base of the cartridge casing.

An example of an ammunition stamp.

- Source: FederalPremium.com

Ballistic Databases

Forensic Technology Inc., a Canadian company located in Montreal, Quebec, has developed a computerized ballistic fingerprinting system called Integrated Ballistic Identification System (IBIS). IBIS creates digital images of the markings left on bullets and shell casings. This allows them to be compared easily to a database of images. When the system finds a bullet or cartridge casing that has similar markings, firearms experts compare these markings to the original evidence to determine whether a match has been made. IBIS minimizes the amount of time firearms experts spend viewing non-matching evidence. Consequently, law enforcement agencies are able to discover links between crimes more efficiently.

The nature of a wound caused by a particular bullet can provide clues to help identify the type of firearm used by the suspect. Numerous factors related to the ballistic properties of a bullet can influence wound characteristics.

Kinetic Energy, Mass, Velocity, and Tumbling: As a bullet travels towards its target, it spirals through the air similar to a football thrown by a quarterback. This is due to the influence of lands and grooves in the gun barrel causing the bullet to spin as it exits the barrel. A bullet is said to tumble if it flips end over end as it approaches its target. A bullet that tumbles has more kinetic energy; therefore, it can cause a more serious injury. A light, high velocity bullet (such as a .223 rifle round) begins tumbling rapidly in tissue. This causes a pronounced cavitation or large wound resulting from the relatively large amount of kinetic energy that is transferred from the bullet to the target.

A bullet’s kinetic energy is dependent upon its mass, its velocity, and whether it tumbles as it moves. Recall the formula for kinetic energy (E_k=1/2mv² ): the faster a bullet is travelling when it strikes the target or the greater the mass of the bullet, the more kinetic energy that bullet will have and the more serious the tissue damage will be. However, if a bullet exits the target, it retains some of its kinetic energy and, therefore, causes less damage.

Bullet Design: As a bullet enters an object, the bullet expands in diameter, a process referred to as the mushroom effect. This expansion releases a bullet’s kinetic energy within an extremely short period of time and causes significant tissue damage. Hollowpoint bullets expand upon impact, especially when travelling at over 305 m/s.

Distance to Target: The distance between the muzzle of a firearm and the intended target has a large role in the kinetic energy a bullet loses during its flight. The kinetic energy lost by the bullet also depends on the type of firearm and the type of cartridge used. For example, most bullets fired from handguns lose significant amounts of kinetic energy after 100 metres; high-velocity military rifle rounds still possess considerable kinetic energy at distances of 500 metres or more. Compared to a handgun round, a rifle bullet possesses more kinetic energy over long distances because its cartridge contains more gunpowder which increases the amount of kinetic energy transferred to the bullet and therefore, increases the velocity of the bullet.

Type of Tissue: The severity of a bullet wound depends on factors such as tissue density and elasticity. Tissues that are more dense (such as bone) tend to sustain more tissue damage, This is because the bullet may fragment and/or cause fragmentation of the bone. Organs such as the liver, spleen, and kidney are relatively inelastic and are easily injured. Fluid-filled organs such as bladder, heart, large blood vessels, and intestines may rupture when struck by a bullet because of the cavitation produced by accompanying shock waves. Conversely, highly elastic tissue suffers less damage. For example, lung tissue, which is more elastic than other internal organs, usually fares better than other tissues when struck by a bullet.

- Image Source: Wikipedia

The assassination of John F. Kennedy, the thirty-fifth President of the United States of America (USA), occurred on Friday, November 22, 1963. Because he was fatally wounded by two gunshots, ballistic evidence was important in the forensic investigation.

The Assassination

President Kennedy was riding in an open-top limousine in a presidential motorcade through Dallas, Texas. The President’s wife (Jacqueline), Texas Governor John Connally, Governor Connally’s wife, and a driver were also in the vehicle. After Kennedy’s limousine slowly passed a building called the Texas School Book Depository, three shots were fired at the limousine from a distance of approximately 60 metres.

As President Kennedy waved to the crowd on his right, the first bullet entered his upper back, exited through his throat, and entered Texas Governor John Connally, penetrating his back, chest, and right wrist. The second bullet missed the vehicle, but the third bullet struck the President in the back of the head. After the three shots, the driver of the President’s limousine sped to a local hospital in a desperate attempt to get emergency medical treatment for the President and the Texas Governor. The President died before arriving at the hospital, and the Governor survived after receiving emergency surgery.

The Investigation

The Dallas Police immediately began searching the area for signs of the assassin. Witnesses claimed the shots came from a nearby building called the Texas Book Depository. Subsequently, police officers found an Italian bolt-action rifle on the sixth floor of the Texas Book Depository. A witness who saw the male assassin fire the last shot from the building gave police a physical description. Police determined that the person that matched the description might be an employee of the Texas Book Depository named Lee Harvey Oswald.

A few hours after the assassination, Dallas Police Officer J. D. Tippit, after hearing the assassin’s description, stopped Oswald on a street corner. When Officer Tippit tried to question Oswald, Oswald shot Tippit four times with a revolver. Oswald fled the scene on foot, and Tippit died from his gunshot wounds. Oswald went into the nearby Texas Theater without paying. The police quickly arrived and arrested Oswald after being notified by theatre staff.

Oswald was questioned for twelve hours about both the Tippit shooting and the assassination of the President. He denied any involvement with the murders. Paraffin tests were performed on Oswald's hands and right cheek for gunpowder residue. The results were positive for the hands and negative for the right cheek.

Two days later as Lee Harvey Oswald was being taken to the Dallas County Jail, he was shot and killed by Jack Ruby before live TV cameras in the basement of Dallas police headquarters.

An official investigation by the Warren Commission conducted in September 1964 concluded that Lee Harvey Oswald was solely responsible for the assassination of President Kennedy.

Internal Ballistic Evidence

The bullet that hit President Kennedy in the head imploded upon impact. As a result, the bullet could not be analyzed for rifling impressions.

However, the bullet that hit Kennedy and Governor Connally was found at the hospital. The bullet was a 6.5 mm round-nose military-style full-metal jacket design specifically meant to pass through the human body. Important pieces of ballistic evidence related to this bullet found by the FBI include the following:

• Neutron Activation Analysis (NAA) of the bullet fragments in Governor Connally’s wrist matched the bullet found.
• The mass of the bullet found was 10.28 g. The average mass of a single, unfired bullet of this type is 10.42 g. The lead fragments retrieved from Connally's wounds in the wrist weighed about 0.13g.
• Rifling impressions found on this bullet matched the lands and grooves in the rifle found at the Texas Book Depository.

External Ballistic Evidence

The muzzle velocities of the bullets that hit President Kennedy were calculated to be between 560 and 610 m/s. Each bullet arced downward while traveling and hit President Kennedy at an angle of 25 degrees from the horizontal.

Terminal Ballistic Evidence

The first bullet that hit the President entered his upper back above the shoulder blade, passed through the base of his neck, bruised the upper tip of his right lung without puncturing it, and exited the front of his neck. The entry point of the bullet was 4 mm by 7 mm in size, and the exit wound was 3 mm by 5 mm. The bullet fractured one of the President’s vertebrae.

Upon leaving the President’s neck, the bullet’s velocity had slowed to about 457 m/s and it had started to tumble. It then hit Governor Connally who was sitting in front of Kennedy. The bullet entered Connally's back creating an 8 mm by 15 mm entry wound. This large entry wound indicates that the bullet was tumbling greatly, which often happens after hitting a target, which was President Kennedy in this case. The bullet destroyed part of one of Connally's ribs as it smashed through his chest leaving an exit wound with a diameter of 50 mm. Slowed to 274 m/s, the bullet entered Connally's upper right wrist depositing metal fragments and exited his palm.

The autopsy of President Kennedy concluded the wound from the second bullet that hit his head was fatal. A small entry wound was visible in the rear right-hand side of the President’s head. The bullet imploded upon impact causing a large portion of the right side of Kennedy’s brain and skull to detach.

Crime Case Study Related Questions

1. Of the two bullets that hit President Kennedy and Governor Connally, why was only one analyzed for ballistic fingerprints?
   Ans.  The bullet that hit the President in the head imploded into fragments upon impact, and therefore, could not be analyzed.
2. What three pieces of ballistic evidence linked the bullet from Connally’s leg to the rifle from the Texas Book Depository?
   Ans. 
   1. NAA of the bullet fragments in Governor Connally’s wrist matched the bullet found.
   2. The mass of the bullet found was 10.28 g and the mass of lead fragments retrieved from Connally's wrist was 0.13 g. The average mass of a single, unfired bullet of that calibre and type is 10.42 g.
   3. Rifling impressions found on this bullet matched the lands and grooves in the rifle found in the Book Deposiory.
3. Answer the following:
   1. How much did the bullet’s velocity change between when it hit Governor Connally in the back to when it entered his wrist?
      Ans.  457 m/s – 274 m/s = 183 m/s
   2. Explain why this change occurred.
      Ans. As the bullet smashed through his flesh and bone (rib), it began losing some of its kinetic energy and slowing.

4. When the first bullet hit President Kennedy, it created a 4 mm x 7 mm entry wound. After it left the President’s body, this same bullet hit Governor Connally creating an 8 mm x 15 mm entry wound. Explain why Governor Connally’s entry wound was so much larger than the President’s entry wound.
   Ans.  As the bullet moved through the President’s neck, it began losing kinetic energy and slowing, causing it to tumble before it hit the Governor. This tumbling caused the Governor’s entry wound to be significantly larger than the President’s entry wound.

Testing for Gunshot Residue

When the trigger of a gun is pressed, the firing pin strikes the primer (5) at the base (4) of the cartridge. This causes a combustion reaction that produces flames. These ignite the gunpowder or propellant (3). The burning gunpowder produces a large amount of gas that propels the bullet (1) from the gun barrel, leaving the casing (2) behind.

Gunshot residue is composed of two substances: a propellant and a primer. Each of these is a solid mixture made of various chemical compounds. The two types of propellants are black powder and smokeless powder.

Black powder consists of charcoal (15%), sulphur (10%), and potassium nitrate (75%). When black powder is ignited, about 55% of its products are solids (soot). The remaining 45% is a gaseous thick black smoke. The soot left behind corrodes the interior of the gun, and the thick smoke reduces accuracy because the target may be obscured.

Smokeless powder is the name given to a number of gunpowder-like propellants that do not produce smoke when fired because their product is mainly gas. All modern ammunition uses smokeless powder. Various types of smokeless powder contain either nitrocellulose (single-based powder) or nitrocellulose mixed with nitro-glycerine (double-based powder).

A primer is a mixture of chemical compounds located in the base of a cartridge. It ignites when subjected to great pressure such as when struck by the firearm’s firing pin.

Several types of primers are available, but the most common are lead(II) azide, lead(II) styphnate, mercury(II) fulminate, barium nitrate, potassium chlorate, and antimony(III) sulphide.

Whenever a gun is fired, the shooter gets sprayed with an invisible blast of chemical residue that consists of the by-products of the incomplete combustion of gunpowder and primer. These products of combustion are deposited on areas of the exposed hand, arm, face, and clothing—right or left side, depending on how the gun was held. The deposited material is known as gunshot residue (GSR), detectable on a person’s skin and clothing to determine if that person has fired a gun.

Because many different types of chemical compounds are in both gunshot residue and primer residue, many testing techniques can be used to detect them. Each of the GSR chemical tests identify unique elements, ions, or compounds. Gunpowder consists of charcoal, sulphur, potassium nitrate, nitrocellulose, nitro-glycerine; primers consist of lead(II) azide, lead(II) styphnate, mercury(II) fulminate, barium nitrate, potassium chlorate, and antimony(III) sulphide.

Paraffin Test

This chemical test is also known as the dermal nitrate test or diphenylamine test. In this procedure, the hands of the suspect are coated with a layer of paraffin. After cooling, the paraffin casts are removed and treated with an acidic solution of diphenylamine. This solution detects two polyatomic ions (nitrites and nitrates) that originate from gunpowder or primer. A positive test produces blue flecks in the paraffin in response to deposits on the hands of the shooter.

Sodium Rhodizonate Test

The sodium rhodizonate test is designed to determine if barium or lead residue are present on the hands. In this test, the hands of the suspect are swabbed with gauze moistened with dilute hydrochloric acid. Then, the gauze is cut into small pieces and drops of sodium rhodizonate, distilled water, and a buffer solution are added to each piece.

A colour change indicates that a salt has formed from rhodizonate and either barium or lead. If the gauze turns a brown-pink, barium was present on the hand. If the gauze turns a scarlet red, then lead was present. A mixture of both these colours indicates that both elements were present.

Harrison-Gilroy Test

The Harrison-Gilroy Test checks for the presence of barium, antimony, and lead on the hands. In this chemical test, the hands of the suspect are swabbed with gauze moistened with dilute hydrochloric acid. The gauze is allowed to dry and then treated with the chemical reagent triphenylmethylarsonium iodide. If antimony is present, the triphenylmethylarsonium iodide turns an orange colour.

Modified Greiss Test

The Modified Greiss Test detects the presence of nitrite residues near suspected bullet holes on a surface such as wood, metal, furniture, clothing, belt, hat, shoes, or purse. Nitrite residues are a common by-product of the combustion of smokeless gunpowder.

In this test, a piece of photographic paper is treated with a chemical mixture of sulfanilic acid and alpha-naphthol in methanol. As a result, the photographic paper is no longer light-sensitive, but it is reactive to the presence of nitrite residues. Then, the paper is placed face down against a suspected bullet hole. The back of the photographic paper is steam ironed with vinegar instead of water in the iron. Vapours from the vinegar penetrate the paper, and a reaction occurs between any nitrite residues on the suspected bullet hole and the chemicals in the treated paper. One of the products of the resulting reaction appears as red and/or orange specks on the photographic paper.

X-ray Analysis with a Scanning Electron Microscope (SEM)

The scanning electron microscope method using X-ray analysis is considered the most reliable and useful way to test for gunshot residue because it can detect any type of element, ion, or compound. This testing procedure is especially helpful when used to confirm the results of one of the other GSR chemical tests. The false negative rate is only 10% for pistols, but it is 50% for long guns.

Samples taken from the hands are analyzed with a scanning electron microscope. X-rays within the microscope are capable of identifying individual particles. Because the scanning electron microscope is an expensive piece of equipment requiring highly specialized experts, not all police departments are able to use X-ray analysis. However, using this method to analyze a sample is possible up to twelve hours after the shooting.

Validity of Gunshot Residue Analysis

Positive GSR test results alone never prove the guilt of a suspect in a court of law. However, when these results are combined with other valid pieces of evidence, gunshot residue test results are powerful.

The strongest conclusion that can be made using only gunshot residue test results is that a suspect recently fired a gun, handled a recently discharged gun, or was close to a gun when it was fired. If the suspect’s fingerprints are also found on a gun, a positive GSR test is compelling evidence that the suspect fired that gun. However, a negative GSR test does not necessarily prove that a suspect did not fire a weapon.

The elements, ions, and compounds such as nitrate, nitrite, or lead that GSR tests identify are not unique to guns and cartridges. Although it is unusual, these substances can also be found in the environment. A person who has not fired a gun but has been near the shooter or the gun after it has been fired can become contaminated with gunshot residue. This is known as secondary transfer. Based on these issues, defence lawyers debate the reliability of GSR evidence in court.

Forensic experts conducting GSR testing are aware of potential contamination problems. Therefore, a positive test for GSR is typically not seen as conclusive unless three or more unique elements or compounds have been detected.

The Murder

In 1999, Robert Blake had an intimate relationship with Bonnie Lee Bakley, a woman with a history of exploiting wealthy older men for money. When Bakley became pregnant and told Blake that he was the father, he ordered a DNA test to determine his paternity. After DNA tests proved that he was the biological father, Blake married Bakley in November 2000. This was Blake’s second marriage and Bonnie Lee Bakley’s tenth marriage.

Five months later on May 4, 2001, Blake took Bakley to a restaurant for dinner. Later, Bakley was murdered by a gunshot to the head while sitting in Blake’s car, which was parked on a side street around the corner from the restaurant. Bakley was shot once in the right cheek and once in the shoulder. Blake told the police that he had walked his wife to his car and then returned to the restaurant because he had left his revolver (which he carried for protection) under a booth. He said that, when he returned to the car, he found Bakley dead.

The Investigation

No witnesses of the shooting were available. No one at the restaurant remembered seeing Robert Blake return to get his gun.

Detectives swabbed Blake for gunshot residue about two and a half hours after the murder. Five particles of gunshot residue were found on his hands, and more residue was found on his black T-shirt, blue jeans, belt, and boots.

The murder weapon was found the next morning in a garbage dumpster about 6 m from Blake’s car. It was an antique 9 mm Walther P-38 double-action, semi-automatic pistol that had been standard issue for the German army in World War II. The gun had no registered owner, and no fingerprints were found on it.

Months into the investigation, police interviewed two retired stuntmen. Both claimed that Blake tried to hire them to kill his wife.

After nearly a year of investigation, Robert Blake was arrested and charged with the murder of his wife. His long-time bodyguard, Earle Caldwell, was also arrested and charged with conspiracy to commit murder.

The Criminal Trial

After spending almost a year in jail, Robert Blake was granted $1.5 million bail and allowed to go free while awaiting trial.

One key piece of physical evidence at the trial was the gunshot residue found on Blake. Defence lawyers argued that this gunshot residue could have come from the gun he picked up from the restaurant. They also argued that the source of the gunshot residue could have been any surface upon which there was gunpowder. Ultimately, the jurors agreed that the presence of gunshot residue on Blake did not necessarily prove that the murder weapon was ever in his hands.

On March 16, 2005, Blake was found not guilty of the murder of Bonnie Lee Bakley and not guilty of soliciting a former stuntman to murder her.

After the Trial

In late 2005, Bonnie Lee Bakley's four children filed a civil suit against Robert Blake stating that he was responsible for their mother's death. A jury found Blake liable for the wrongful death of his wife and ordered him to pay $30 million. This lead Blake to file for bankruptcy in early 2006. Blake’s and Bakley’s young daughter, Rosie, was adopted by Blake’s eldest daughter.

Related Questions:

Criminal Case Study: The Mysterious Murder of a Hollywood Star’s Wife

• During the investigation of Robert Blake, where did detectives locate the gunshot residue?
  

• Where did Robert Blake’s attorneys claim the gunshot residue found on him could have come from?
  

• “How valid gunshot residue test results are seen by a jury depends a lot upon on how convincing the other evidence in the case is.”
  

  Explain how this statement applies to the Robert Blake case.
  

• Why did Robert Blake file for bankruptcy in 2006?
  

Overview

The Duke Projectile Recovery System (below) allows forensic ballistic experts to test-fire a gun and retrieve the bullet intact for ballistics forensic firearm identification.

This lesson focuses on two criminal case studies that involve forensic ballistics.

You are expected to answer related questions about these criminal case studies in your assignment.

A firearms identification expert with the U.S. Bureau of Alcohol, Tobacco, and Firearms holds the Bushmaster rifle used in the Beltway Sniper shootings. - Image Source: Tracy Woodward / AP pool                                                                                                                                                      - Journal Source: Muhammad trial journal by Kerry Sipe

During September and October 2002, a series of random shootings terrorized the public along the east coast of the United States. The murders were coined the Beltway sniper killings because the majority of the shootings occurred near a freeway called the Capital Beltway in Maryland, Virginia, and Washington, D.C. The shooter used a high-powered rifle from a concealed location approximately 100 m or less away from each victim. Thirteen people were killed, and three people were critically injured while in various outdoor public places. Ballistic evidence played a critical role in the capture and conviction of the two males responsible for the shootings and it was later discovered that the pair was also responsible for sniper attacks in California, Arizona and Texas.

Identity of the Snipers

The older of the two men responsible for the Beltway sniper killings was John Allen Williams. After converting to Islam, he changed his name to John Allen Muhammad in 2002. A 41-year-old ex-member of the United States National Guard and the United States Army, he had earned medals for expert marksmanship while serving in the army.

The younger of the two Beltway snipers was 17-year-old Lee Boyd Malvo who also used the name John Lee Malvo. He had posed as John Allen Muhammad's son, but he was the son of a woman with whom Muhammad had a friendship. Malvo shoplifted the rifle used in the sniper shootings from a gun dealer in Tacoma, Washington.

The Shootings

On September 5, 2002, a pizzeria owner died after being shot six times at close range while closing his restaurant in Maryland. His laptop computer was found in the suspect’s car when they were arrested later.

On September 21, a liquor store clerk in Alabama was shot and killed during a robbery, and a co-worker was injured.

On October 2, a 55-year-old program analyst was shot and killed in a grocery store parking lot in Maryland.

October 3 was the deadliest day. Within a 15-hour period, four people in Maryland and one in Washington, D.C., were shot and killed. The first victim was a 34-year-old man shot while mowing a lawn. Then, a 54-year-old taxi driver was killed while pumping gas into his taxi. The third victim was a 34-year-old woman shot while reading a book on a bench. The fourth victim was a 25-year-old woman shot while vacuuming her van. The fifth victim was a 72-year-old retired man shot while walking down a street in Washington, D.C.

On October 4, a 43-year-old woman was shot in a shopping centre parking lot; fortunately, she survived.

On October 7, the public was shocked when the Beltway sniper shot a 13-year-old boy walking into his school in Maryland. The boy lost 25 to 30% of his blood. One of his lungs, his diaphragm, part of his liver, stomach, pancreas, and spleen were damaged. Incredibly, after emergency surgery, the boy survived after spending eight weeks in hospital.

The next two shootings, October 9 and 11, were strangely similar despite happening two days apart. In both instances, 53-year-old males were shot and killed while pumping gas at a gas station in Virginia.

On October 14, a 47-year-old FBI intelligence analyst from Virginia was shot dead outside a Home Depot store.

Five days later, a 37-year-old man was shot in a parking lot outside a restaurant in Virginia.

A bus driver was shot and killed while standing outside his bus on October 22—making thirteen dead and three injured.

The Investigation

After each shooting, roadblocks were set up near the crime scene. Cars and drivers were inspected as they passed through each roadblock, resulting in massive traffic jams. Despite these efforts, police discovered later that the suspects had gone through these roadblocks several times and had not been caught.

At several crime scenes, Tarot cards and handwritten notes were left by the suspects. One tarot card was the Death card upon which was written, "Dear Policeman, I am God. Do not tell the media about this." The handwritten notes were several pages long and carefully sealed inside plastic bags. One of the notes demanded $10 000 000. It stated, "Your children are not safe, anywhere, at any time."

On October 21, a fingerprint from the September 21 Alabama shooting was found and identified. The print belonged to 17-year-old Lee Boyd Malvo. Investigators learned that Malvo was in the company of John Allen Muhammad. Police issued a description of Muhammad’s dark blue Chevrolet Caprice sedan to the media.

Investigators then discovered that Malvo and Muhammad had recently been staying at a home in Tacoma, Washington. A tree stump from the yard of this home, believed to have been used for target practice by the suspects, was seized. Metal detectors were used to search for bullet and cartridge casings in the yard to try to link the suspects to the shootings.

On October 24, two separate citizens reported a blue Chevrolet Caprice sedan parked at a rest area in Maryland. John Allen Muhammad and Lee Boyd Malvo were sleeping inside the vehicle and were arrested without incident. A search of the vehicle revealed that the suspects had created a firing port in the trunk of the car. The firing port allowed them to remain hidden while they shot at their unsuspecting victims. After these arrests, the Beltway sniper shootings stopped.

Ballistic Evidence

A Bushmaster .223 semi-automatic rifle and bipod were found in a bag in John Allen Muhammad's car. Bullets fired from this rifle had an average muzzle velocity of 960 m/s. A bullet fired at this high velocity disintegrates when it hits bone or tissue leaving behind hundreds of bullet fragments (see photo below). In an X-ray, these numerous bullet fragments form a pattern known as the snowstorm effect. The snowstorm effect was visible on X-rays of each of the Beltway sniper’s victims.

The recovered bullet fragments and cartridge casings were compared to 150 different guns. Ballistic experts were unable to link any of those weapons to the crime scene evidence. The bullet fragments and cartridge casings from the shootings were then compared to test bullets fired from the rifle recovered from Muhammad’s car. Ballistic experts concluded that 11 of the 14 bullet fragments recovered from the shootings matched the rifling impressions from the rifle seized from the suspect’s car.

A forensic chemist found both gunpowder residue and primer residue in the trunk of Muhammad’s car. The presence of these chemicals indicated that a gun was likely fired from inside the trunk.

Although not considered ballistic evidence, numerous amounts of DNA matching both Malvo and Muhammad were identified on several areas of the rifle found in the suspects’ car.

Conclusion

John Allen Muhammad and Lee Boyd Malvo were tried separately in both Maryland and Virginia.

In 2003, after more than 130 witnesses and 400 pieces of evidence, Muhammad and Malvo were each found guilty for the shootings that occurred in Virginia. Muhammad was sentenced to death, and Malvo's jury gave him a life sentence without parole.

In 2006, Muhammad was extradited to Maryland and found guilty of six counts of first-degree murder. He was sentenced to six consecutive life terms without the possibility of parole. Malvo pleaded guilty to these six murders and was also given six consecutive life terms without parole.

• maintaining a safe distance
• seeking cover (shielding)
• movement to a safe area from which to contain the suspect.

Ideally, a police officer will seek cover (rather than concealment) behind which he or she can maintain visual contact with a suspect. This way, if the officer is fired upon, he or she is not an easy target. Moving to cover or gaining distance from the suspect is also effective if the officer is not in a position to seek immediate cover.

Identifying the type of firearm being used by a suspect is important when considering the principles of distance, shielding, and movement. Often, distinguishing among a revolver, semi-automatic pistol, shotgun, and rifle is possible. Confronting a suspect who has a rifle rather than a small handgun means that officers must be especially careful when choosing cover because rifle bullets can penetrate many materials that handgun bullets cannot.

Early Morning Robbery

At 5:30 on a Sunday morning, a silent alarm is received by police from a local convenience store located in a quiet neighbourhood in a large city. Several violent robberies have occurred in the past month, and this alarm might be related.

Four police officers are available to respond. They travel to the convenience store in two police vehicles. When the patrol units are still about a block away from the store, they receive word that three masked suspects have fled the store and are about to leave in a vehicle. However, police have cut off the only avenue of escape, leaving the suspects with nowhere to go.

The four officers are then notified by radio that one of the suspects shot and killed the lone clerk at the convenience store and may use a firearm to aid in his escape. The officers are in various positions about half a block away. If the suspects decide to escape on foot, police may have to close in on the parking lot to contain the area until additional police units respond.

The suspects step out of their vehicle and begin running across the parking lot. One suspect brandishes a handgun and runs west towards an elementary school. A second suspect, also armed with a handgun, runs north toward a shopping mall. The third suspect runs east into a wooded ravine, carrying what appears to be a shotgun. The officers are still a half block away, but they start to move in on foot to prevent the suspects from escaping.

A police helicopter arrives and is able to track the three suspects, simultaneously broadcasting their locations over the police radio. Another pair of officers, traveling in a marked police cruiser, locates the first suspect hiding in a playground at the nearby school. When officers corner the suspect, he is upset and makes verbal threats that he will shoot if the police close in. Meanwhile, the second suspect runs towards the shopping mall pursued by officers on foot. The officers see the man throw his gun into a dumpster as he enters the building. At the same time, officers on foot follow the third suspect into a ravine.