Handling and processing evidence is an integral component of crime scene management because it lays the foundation for everything the court must consider when weighing the admissibi

1Forensic Science and Criminalistics

Associated Press

Learning Objectives After reading this chapter, you should be able to do the following:

▪ Define forensic science and how it contributes to a case, as well as explain the CSI Effect and the scientific method.

▪ Summarize the history of forensic science and contributors to the field.

▪ List and describe some forensic science specialties.

▪ Identify the elements of a forensic investigation, how physical evidence can be produced, and forensic analysis.

▪ Describe the work and work product of a forensic scientist.

▪ Describe the U.S. court system, and the key rulings on physical evidence admissibility through expert testimony.

▪ List and discuss major issues in forensic science today.

235

Learning Outcomes After reading this chapter, you should be able to

▪ Describe firearms, projectiles, and cartridge casings and the role each plays in investigations.

▪ Describe proper collection and handling of firearms evidence.

▪ Explain firearms analysis and conclusions formed from the evidence.

▪ Describe gunshot residue and how it is analyzed.

▪ Identify tools, their marks, and how this evidence is collected and analyzed.

▪ Explain how documents are collected and analyzed.

Steve Helber/Associated Press

Pattern Evidence II: Firearms, Tool Marks, and

Documents Analysis

9

© 2019 Bridgepoint Education, Inc. All rights reserved. Not for resale or redistribution.

Introduction

Introduction This chapter continues the discussion of patterns for individualization. It will specifically cover firearms and tools used in cases involving forensic analysis and disputes that arise about the authenticity or author of a document in evidence. The major premises for these identifications are that no two guns make identical markings on bullets and cartridge cases and that no two people have identical handwriting.

Many of the analyses completed in these areas of forensic science depend on agreement of class characteristics, followed by individual characteristics, in that order. In Chapter 1.4 we defined class and individual characteristics. We talked about them again in Chapter 8.3. Let’s review these concepts briefly in the context of this chapter’s subjects. A class characteristic places several items in the same category because they are the same in some way. For exam- ple, if an examiner is analyzing a document to see if a suspect may have written it, analysis could be run on the ink on the paper. The results will connect the ink to a particular manufac- turer of pens. If the suspect owned or used that type of pen, he or she could be included—but so could anyone else who used that type of pen.

In firearms analysis, class characteristics are also very important because of their ability to narrow the focus of a case. Class characteristics in firearms cases are determined by the manufacturer. They can include the number and width of lands and grooves in the barrel of a gun, the direction of twist, and the caliber of the gun. The firearms analyst can quickly include or exclude a particular weapon as having fired a bullet through comparison of these manufactured characteristics. A cartridge is an unfired case containing a bullet. Once it has been fired in a weapon, it is a cartridge case, or cartridge casing. Cartridge casings can also be examined using class characteristics to identify the caliber and features of the weapon for which they are intended. There are center-fire and rim-fire cartridges, and cartridge cases from semiautomatic weapons will have extractor and/or ejector markings. (The exception to these analyses is shotgun ammunition, as will be discussed later). With firearms identifica- tion, individual characteristics are specific to a particular weapon.

Individual characteristics are random in nature. In documents analysis, the way a person writes is the product of years of development, to the point that the writer is unconscious of his or her handwriting. Unconscious writing has combinations of characteristics that can make it easily identified. In terms of individual characteristics for firearms, the machines used to put the grooves into the barrel of a gun change over time and impart microscopic striations to the barrel. These striations, seen within the rifling in a barrel, transfer to the surface of the bullet and can be compared to a known bullet fired from a particular gun. The same acciden- tal microscopic markings can be found on many tools, such as the tip of a screwdriver. All of these microscopic imperfections can be transferred to another surface and compared back to the tool that made them.

In summary, comparison of class characteristics allows examiners to narrow the focus to a set, or class, of items, while the individual characteristics will allow them to tell which, if any, item in the set left the markings behind. We will first look at the comparison and identifica- tion of firearms in forensic science. It should be noted here that the markings on bullets and cartridge cases from guns are a type of tool mark. That is, tool marks represent the broader general category. But non-firearm-related tool mark cases are less frequent in forensic case- work. (You could also think of bite marks, which we discussed in Chapter 8, as a type of tool mark, where human teeth are the tool.) A terminology note: Comparing bullets and cartridge

© 2019 Bridgepoint Education, Inc. All rights reserved. Not for resale or redistribution.

Section 9.1Firearms

cases with test fires from particular weapons to find the weapon that fired the questioned bullet is called firearms identification and is not equivalent to ballistics. Ballistics is the phys- ics of projectile flight through the air from barrel to target. Ballistics can come up in recon- structions involving fired weapons, but it is not the same thing as firearms identification.

There is one kind of trace evidence that we did not discuss in Chapters 6 and 7, because it is closely associated with firearms: gunshot residue. This topic will be included here.

9.1 Firearms Over the years, research and development in firearms has concentrated on increasing their range and accuracy. Propellants, the materials used to generate enough force to propel the bullet, were improved for range, but one of the most fortuitous developments involved rifling in the barrels of the firearms. The rifling in a barrel of a gun resembles the striping of a candy cane, a spiral of raised and lowered areas on the inner surface of the barrel of a firearm. Rifling, shown in Figure 9.1, imparts spin to the projectile. A projectile is defined as some- thing that can be propelled—in the case of firearms, a bullet. When a projectile is spinning, it is very similar to a top. While unstable and easily knocked over when not spinning, a top is very stable when spinning and tends to remain upright. This spin, when imparted to a fired projectile, will result in stability that increases accuracy over a longer range. Some firearms examiners have compared this to a quarterback throwing a football. If the football spirals, it will travel a greater distance with more accuracy than one thrown end over end. Rifle and pistol barrels are rifled. Shotgun barrels are not.

Figure 9.1: Rifling of a gun barrel

The barrel of a firearm has spiral cuts called rifling, which is made up of a series of lands and grooves. This allows the bullet to travel farther and with more accuracy.

Before the inclusion of rifling in the barrel of a firearm, a bullet comparison was accomplished by comparing the caliber of a projectile to a possible firearm manufacturer. The use of rifling in the barrels of firearms has not only improved accuracy and range, it has had the added benefit

Groove

Land

© 2019 Bridgepoint Education, Inc. All rights reserved. Not for resale or redistribution.

Section 9.1Firearms

of imparting macroscopic and microscopic markings onto the fired projectiles. The macro- scopic markings are easily seen with the naked eye and represent the lands and grooves in the barrel of the firearm. Lands are the raised portions of the barrel and are what remains of the original surface of the barrel before the grooves were formed. The grooves are the lowered spaces between the lands. These are some of the class characteristics that an examiner will use to determine if a particular class of weapon is involved in a case. The microscopic mark- ings represent the individual characteristics the examiner will use to determine if a particular weapon in the class fired the projectile. These are also known as striations on the bullet.

Striations found in a gun barrel result in individualized patterns that may be unique among the members of their class and can be found on the fired projectile. If all class characteristics are the same, the analyst can compare the striations. If sufficient information matches between the evidence and a known standard generated by the analyst, he or she can say the two items came from the same gun. There are several other conclusions that can be reached by the ana- lyst. If class characteristics do not match between a bullet fired from a suspect’s weapon and the evidence bullet, the analyst can exclude the item, since individual characteristics cannot match if class characteristics do not match. If class characteristics match between the stan- dard and evidence but there is not enough information to form a definite link between the evidence and standard, the analyst can call the results inconclusive. This type of analysis has been accepted in the courts since the early 1900s (National Institute of Justice, n.d.).

The idea of this type of analysis might be hard to visualize. How did those markings get into the barrel of the gun or, in the case of cartridge cases, onto the firing pin and breech face (the back end of the barrel of the gun, which helps contain the explosive forces released upon fir- ing)? How are they individualized? These things relate to the manufacture of the firearm itself.

The rifling in the barrel of a firearm is produced by one of three main methods—the broach- cutting, button, and mandrel methods. In the broach-cutting method, blades are used to shave metal from the inside of a metal tube, which will become the barrel of a firearm. These shaved areas become the grooves in the barrel of the firearm. The unshaved interior surfaces of the tube that remain become the lands of the barrel. Each time the blades are used, microscopic imperfections on the blades change with use. These microscopic imperfections leave mark- ings that are impressed into a projectile as it travels down the barrel of the firearm.

The button method involves the use of a metal plug, formed to represent the negative of what will be the final configuration of the inside of the gun barrel. The barrel is formed by pushing or pulling the button through the length of the metal tube that will become the barrel in a spi- ral motion, pressing the grooves into the tube. Due to the pressures involved, the compressing surface of the button changes at the microscopic level and leaves different microscopic imper- fections along the grooves of each barrel created.

The last method of forming a barrel for a firearm uses a mandrel, or rod, that has been formed to be a negative of the gun barrel. This rod is inserted into the tube that will be the gun bar- rel. Hammers compress the tube around the rod. When complete, the mandrel is twisted out of the newly formed barrel. Again, pressures exert stress on the barrel and the rod. The rod changes with each use at the microscopic level and leaves imperfections on the inside of the gun barrel that will be transferred to bullets that are fired through the firearm. The imperfec- tions that each rifling method produces are what can be used to individualize a firearm.

There is another point of terminology worth mentioning here. When a firearms, tool mark, or questioned document examiner says “identification,” he or she means “individualization.”

© 2019 Bridgepoint Education, Inc. All rights reserved. Not for resale or redistribution.

Section 9.1Firearms

Two old cases were exceptionally instrumental in the development of the firearms identifica- tion field in the United States: The Sacco and Vanzetti case in Massachusetts and the St. Valen- tine’s Day massacre in Chicago.

Case Illustration: State of Massachusetts v. Sacco and Vanzetti On April 15, 1920, there was a daring robbery of a cash payroll in South Braintree, Massachusetts. In those days, factory employees were paid in cash. Two men were killed as they were transporting payroll cash to the factory at the time of the robbery. Police atten- tion focused on Nicola Sacco and Bartolomeo Vanzetti, not only for the Braintree robbery but also for another earlier holdup. The getaway car may have been the same one in both cases. When arrested, Sacco had a .32 Colt semiautomatic pistol. Test firings and compari- sons matched that gun to a bullet taken from the body of Berardelli, one of the murdered payroll guards. A firearms examiner from the Massachusetts State Police testified at the trial. In 1921 both defendants were convicted of murder and sentenced to death. The fire- arms evidence was the only forensic evidence in the case, and firearms identification was in its infancy at the time. After voluminous postconviction legal proceedings, both men were executed in 1927.

Sacco and Vanzetti were anarchists; they believed that the government should be over- thrown by violent means, if necessary—a fact that did not help their case. There have been several reexaminations of the bullet evidence, and it has always been verified that the questioned bullet from Berardelli’s body was fired by the .32 Colt handgun. However, allega- tions of tampering with the bullets and the gun have arisen over the years, and the chain of custody is not very accurate or verifiable. Many people believe that Sacco and Vanzetti were arrested, convicted, and executed mainly because they were anarchists and that this case was in fact a miscarriage of justice. This provides a classic example of how chain of cus- tody needs to be solid in any forensic case, especially in a capital case, which often involves firearms.

Reflect On It The firearms evidence was the only forensic evidence in this case, although the chain of cus- tody cannot be verified. Due to this, do you think the verdict would be the same today? Why or why not?

Case Illustration: State of Illinois v. Capone The St. Valentine’s Day massacre occurred on February 14, 1929, at a garage at 2122 N. Clark Street in Chicago. This crime was gang related, and the well-known gangster Al Capone was behind the murders. Five members of a rival gang were lined up against the wall of a garage and massacred using Thompson submachine guns. The perpetrators were dressed in Chicago Police uniforms, which is how they lured the victims into the location. Police were eventually able to solve the case and tie it to the Capone gang. Bullets and cartridge cases were collected from the scene, along with the weapons, and were examined by Colonel Calvin Goddard. He was able to associate the machine guns with the fired evidence.

After years of tolerating violent gang activity in Chicago, the public had had enough with the Chicago mob and their violence. Gang activity declined in the city. Goddard’s involvement in this case led to the formation of a firearms identification laboratory at Northwestern

(continued on next page)

© 2019 Bridgepoint Education, Inc. All rights reserved. Not for resale or redistribution.

Section 9.1Firearms

Types of Firearms There are several major types of firearms that are seen in forensic laboratories. These include different types of handguns and long guns. Handguns, commonly called pistols, are catego- rized into two major types. The first uses a cylinder with several chambers containing the cartridges. This is termed a revolver and is perhaps best represented by the six-shooter. The second type of handgun uses a magazine to hold the cartridges. This magazine is usually contained within the grip of the handgun. This type of weapon is usually termed a semiau- tomatic firearm (pistol) and can be represented by the .45 caliber Colt. Figures 9.2 and 9.3 provide examples of a revolver, a pistol, and their parts.

Figure 9.2: Revolver

A revolver handgun has a cylinder that holds the cartridges. After a cartridge is fired, the cartridge casing stays in the chamber, and the hammer can be pulled back to rotate the cylinder and place another cartridge under the firing pin.

Adapted from “Chapter 2—Firearms and Ammunition,” by Texas Parks & Wildlife, n.d., Retrieved from https://tpwd.texas.gov/ education/hunter-education/online-course/firearms-and-ammunition-1.

Case Illustration: State of Illinois v. Capone (continued) University, which was later transferred to the City of Chicago as its forensic lab. Goddard is considered a founding father of forensic firearms identification in the United States.

Reflect On It Thompson submachine guns can fire a number of bullets in seconds. If you were the exam- iner for the St. Valentine’s Day massacre case, how would you go about analyzing all the fire- arms evidence?

Think About It

There was a backlog of firearms evidence in public labs in the United States as of 2014. Compared with other types of evidence, such as drugs and DNA evidence, the backlog is smaller. Why do you think this is the case? Can you think of some ways to reduce the back- logs in firearms examination?

Chambers

Trigger

Cylinder

Hammer

© 2019 Bridgepoint Education, Inc. All rights reserved. Not for resale or redistribution.

Section 9.1Firearms

Figure 9.3: Semiautomatic pistol

A semiautomatic handgun has a magazine that holds the cartridges. When fired, the slide moves backward, and the cartridge casing leaves through the ejection port. As the slide moves forward, it picks up another cartridge from the magazine and loads it into the chamber.

Adapted from “Chapter 2—Firearms and Ammunition,” by Texas Parks & Wildlife, n.d., Retrieved from https://tpwd.texas.gov /education/hunter-education/online-course/firearms-and-ammunition-1.

There are some differences in the operation of these firearms and the evidence left behind from their use. The revolver operates when the hammer of the firearm is pulled back. This rotates the cylinder one position. A live cartridge is now under the firing pin. When the shooter pulls the trigger, the hammer strikes the firing pin, setting off the cartridge. The bul- let travels down the barrel of the gun, propelled by the expanding hot gases from the burning of the propellant. In order to fire the gun again, the hammer must be pulled back to rotate the cylinder so a new cartridge is in firing position.

There are two types of revolvers. The first, called a single-action revolver, requires manual cocking of the hammer. In other words, the shooter must pull the hammer back to ready the firearm to fire. The double-action revolver allows the shooter to pull the trigger, which simultaneously cocks the hammer, rotates the cylinder, and fires the weapon with one pull. This increases the rate of fire of the pistols. A disadvantage to this type of weapon for forensic work is that unless the shooter has to reload the weapon, cartridge casings will not be left at a crime scene.

SlideSlide

MagazineMagazine

Grip

Muzzle Muzzle

Trigger

© 2019 Bridgepoint Education, Inc. All rights reserved. Not for resale or redistribution.

Section 9.1Firearms

Semiautomatic pistols were developed in the early 1900s. As mentioned, the cartridges are stored in a magazine in the grip of the pistol. When a shooter readies this type of weapon, he or she will pull back the slide, which is located at the top of the frame of the pistol, and release it. As the slide moves forward, it picks up the cartridge at the top of the magazine and slides it into the firing chamber. At this point, the hammer is placed in the firing position. When the shooter pulls the trigger, the hammer strikes the firing pin, setting off the cartridge. The bul- let travels down the barrel of the gun, propelled by the expanding hot gases from the burning of the propellant. At this time, a second action is taking place, the opposite and equal action to propelling the bullet down the barrel of the gun. Remember, the hot gases try to expand in all directions. The firing chamber prevents them from expanding to the sides. Since the slide of the gun is movable, while the bullet is being forced through the barrel, equal and opposite action will force the slide backward. As the slide goes back, the just-fired cartridge casing is ejected from the firearm through the ejection port, and the hammer is cocked. The slide reaches its farthest distance back, comes forward, picks up another cartridge at the top of the magazine and slides it into the firing chamber. The pistol is again ready to fire. When the shooter pulls the trigger, the process repeats.

Semiautomatic weapons require that the trigger is pulled each time the weapon fires. Maga- zines typically hold 8 to 15 cartridges, though some have been designed to hold more. This type of weapon offers a benefit to investigators. Cartridge casings are ejected from the weapon each time it is fired. This evidence can be collected and submitted to the firearms examiner so that even if fired bullets are not found, evidence exists that can help determine the gun used in a crime.

Automatic firearms are weapons that are designed to fire as long as the trigger is held down. These weapons are usually of the true assault weapon variety—or larger—such as machine guns. They are illegal in the United States except under special permits from the BATF, although some people hold these weapons illegally. At crime scenes, they will leave behind the same projectiles and cartridge cases as semiautomatic weapons.

Long guns are designed to be fired using the shoulder for support. There are two main types of long guns seen by investigators: rifles and shotguns. The main difference is that shotguns do not have rifling in the barrel. This means that fired projectiles from a shotgun cannot be compared to test fires from a particular weapon. Ammunition for a shotgun is a shotshell. It usually contains buckshot but can contain a single projectile known as a slug. Once fired, it is a shotshell case or casing. Rifles, on the other hand, have rifling in the barrel, and their projectiles can be used for comparison. The function of these weapons is very similar to that of the handguns. Rifles and pistols are characterized by the diameter of their barrels. In rifled barrels, the diameter is measured land-to-land. This feature is called caliber. Caliber can be stated in inches or millimeters. It is sometimes stated in what might be called firearms slang. For example, a .380 semiautomatic pistol has a barrel diameter of 0.38 inches. But, a so-called .38 special has a barrel diameter of 0.357 inches, the same as a .357 magnum. Caliber is a class characteristic that can also help in identifying a type of firearm.

Types of Projectiles There have been many types of projectiles designed for use in weapons. Among the first were the simple round balls made of lead used in guns before barrel rifling. After rifling was added, bullets were elongated to facilitate use of the rifling to pick up spin. After this, many different

© 2019 Bridgepoint Education, Inc. All rights reserved. Not for resale or redistribution.

Section 9.1Firearms

designs of bullets were used. The designs often reflected their use. Adaptations to the early round lead bullets included flattening the end of the bullet rather than rounding it. This allowed the diameter of the bullet to expand more after it hit the target, doing more damage. After a while, the end of the bullet was hollowed out, forming the hollow-point bullet that was supposed to expand further upon contact with the target. Then metal coverings were added to the projectile. This would limit deformation of the projectile after it struck, allowing more penetration into the target. The effect of design changes of the projectiles was to inflict more damage to the target.

Forensic examiners and law enforcement are not typically concerned with these changes other than how they affect the characteristics of the bullet when it fires. Less deformation will result in a greater chance of a successful comparison between two projectiles. More deforma- tion or actual destruction of the projectile will mean less information available to the exam- iner, precluding comparisons or identifications. An example of this is exploding-tip bullets. This bullet type is hollowed out, and a small explosive charge is placed in the cavity. A small ball bearing is placed in the cavity as well, and the cavity is then sealed. The theory is that when the bullet strikes the target, the ball bearing will be forced into the explosive, causing the bullet to rupture. This will fragment the bullet into pieces small enough that comparisons may not be possible.

Today, instead of lead as the main component of the projectile, metal alloys are used. Some are harder than lead and result in less deformation. Others are frangible, which means they will break apart when they strike their target. In any event, the investigator must be aware of the possible evidence to be found at crime scenes and be prepared for anything from a pristine bullet taken from a wall to fragments taken from a body.

Cartridge Casings In situations in which fired projectiles may not be found, cartridge casings may be very valu- able. If a cartridge casing is collected, it can provide the investigator with some immediate information that will also be important to the firearms examiner. On the back end of the car- tridge casing are markings placed by the manufacturer; these are called the headstamp. The headstamp includes information such as the caliber of the cartridge and the manufacturer. Additionally, the breech face markings from the firearm itself, which may be found on the cartridge casing, can be used to tie it to a particular gun just as easily as a fired projectile. The breech face is essentially the back end of the firing chamber of a firearm. The cartridge case will be forced backward as the bullet is forced out of the barrel by the burning propellant. Breech face markings are marks left on the breech face from the recoil of the firearm. The firearms examiner can make use of several different markings that may be present, such as

Think About It

Which bullet design for a 9 mm semiautomatic pistol do you think would be easier for a firearms examiner to use in comparison after the bullet has been fired and has hit a hard surface: a copper-jacketed hollow point, or a simple, lead flat-nose bullet? Why?

© 2019 Bridgepoint Education, Inc. All rights reserved. Not for resale or redistribution.

Section 9.2Collection and Preservation of Firearms Evidence

extractor and ejector markings, but usu- ally the breech face and firing pin mark- ings are sufficient, since they will provide the individualizing characteristics neces- sary to identify the cartridge case to the suspected firearm.

When the cartridge is detonated, the firing pin strikes the primer. This will leave the impression of the firing pin on the primer. The propellant is detonated and the pro- jectile forced down the barrel of the gun because of the hot expanding gases. At the same time, due to equal and oppo- site actions, the cartridge casing is forced backward into the breechblock. Markings, both microscopic and macroscopic, are impressed onto the back of the cartridge. Again, since these are machined parts, they are individual. Studies have been done to determine the individuality of these markings and their potential for use in casework (Smith, 2005). Bullets, cartridge cases, and shotshell cases are all known as fired evidence.

9.2 Collection and Preservation of Firearms Evidence The evidence, whether it is a bullet, cartridge casing, or gun, needs special care. The fired projectiles and cartridge casings need to be protected from damage and change. In order to do this, the investigator must remember that anytime metal strikes—or even rubs against— metal, marks can be left behind. If all of the cartridge casings collected from a crime scene are placed in the same box or bag with no other protection, those casings will rub together, caus- ing additional marks. Any damage caused by this contact can lower the chances of an exam- iner making an identification. It is the same for the fired projectiles. If placed unprotected in the same package, damage will result.

Several methods of packaging are available. Small coin or jewelry boxes can be used to store individual items. Multiple items can be stored together, as well, if they are individually wrapped in cotton or tissue. The main rule is that metal should not touch metal. In addition, these items cannot be labeled or marked directly. The best method is to package them each in their own individual containers with appropriate numbering and labeling on each package.

Firearms packaging has two goals: protect the personnel handling the evidence and pro- tect the firearm from damage. Firearms seized at a crime scene hav

Collepals.com Plagiarism Free Papers

Are you looking for custom essay writing service or even dissertation writing services? Just request for our write my paper service, and we'll match you with the best essay writer in your subject! With an exceptional team of professional academic experts in a wide range of subjects, we can guarantee you an unrivaled quality of custom-written papers.

Get ZERO PLAGIARISM, HUMAN WRITTEN ESSAYS

Why Hire Collepals.com writers to do your paper?

Quality- We are experienced and have access to ample research materials.

We write plagiarism Free Content

Confidential- We never share or sell your personal information to third parties.

Support-Chat with us today! We are always waiting to answer all your questions.