Crime Laboratories

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Crime Laboratories

Crime laboratories offer forensic science services to the criminal justice system. Forensic science applies scientific testing methods and the latest technologies to collect, preserve, process, and analyze evidence. Proof of guilt or innocence is frequently determined by the results of forensic evidence.

Forensic science is a combination of many kinds of knowledge, some of which have existed, however primitive, for centuries. These include weapon identification, fingerprinting, document analysis, chemical identification, and trace analysis of hair and fibers. Two newer disciplines that have become major components of the twenty-first century crime laboratory are DNA analysis and explosive investigation.

The leading forensic laboratory in the world is at the Federal Bureau of Investigation (FBI), located 50 miles outside of Washington, D.C., in Quantico, Virginia. The FBI Laboratory moved from its site in downtown Washington, D.C., to its newly built facility in early 2003. The FBI Lab, with approximately 650 employees, partners with state and local crime laboratories throughout the country to solve criminal cases.

In this chapter a brief history of forensics is presented, followed by a description of the major types of forensic investigation used in crime labs at the local, state, federal, and private levels. Next is an in-depth look at the FBI Lab, followed by details of how crime lab investigations identified the individuals responsible for a series of sniper attacks that paralyzed the Washington, D.C., area in October 2002.

Historical perspective

The word forensic comes from a Latin term meaning "in the court" or "public forum." Forensic science applies scientific knowledge within a court of law. Forensic science has existed for many centuries. Its beginnings can be traced to thirteenth-century China where in 1248 a scientist wrote a book called Hsi Yüan Lu (The Washing Away of Wrongs). The author tell readers to not be surprised if solving a crime comes down to the difference between two hairs.

Although much of what the author discusses relies solely on superstition, Hsi Yüan Lu clearly demonstrates aspects of forensic detection that are still used today. For instance, the book discusses the importance of analyzing wounds inflicted on a dead body. Most importantly, the book talks about the need to study the scene of a crime. Hsi Yüan Lu teaches that to solve a crime, one must carefully observe all clues.

The Chinese first used fingerprint identification to match documents to their authors in the eighth century. By the nineteenth century four main types of fingerprints were identified: arches, loops, whorls, and composites. Fingerprint patterns proved to be unique to each person. By studying the arches, loops, whorls, and composites, criminalists could compare fingerprints to see if they matched. This idea has not changed and is still the fundamental basis of modern fingerprint technology.

An early famous case of firearm identification came from the Bow Street Runners, a group of policemen in England, who became famous because of their success in catching criminals. In 1835 one of the Bow Street Runners, Henry Goddard, was called to the scene of a shooting. After the lead bullet was removed from the dead man, Goddard examined it and found a distinctive ridge. By comparing the marks on bullets from the firearms from several suspects, Goddard determined the source of the bullet and arrested the guilty party. Following Goddard's lead, many cases involving firearms were solved by the careful analysis of the marks left behind on spent bullets or casings.

Another ancient scientific study involved poisons. The word toxicology comes from the Greek word toxicon, which means poison. Greek physician Hippocrates (c. 460–380 b.c.e.) introduced toxicology by describing the use and effects of poisons. In the Middle Ages (c. 500–c. 1500), an Italian noblewoman named Catherine de Medici (1518–1589) experimented with poisons by giving them to people of the lower class and then recording their reactions. In the nineteenth century a Spanish physician named Mathieu Joseph Bonaventura Orfila (1787–1853) was the first scientist to introduce chemical analysis as proof of poisoning in a court of law.

Crime laboratories

In 1910 Professor Edmund Locard (1877–1966) of the University of Lyons, France, established the first crime lab based upon the idea that criminals leave behind traces of themselves with every crime. Using Locard's principles, Los Angeles, California, police chief August Vollmer (1875–1955) established one of the first modern crime laboratories in the United States in 1923.

Vollmer recognized the need to establish a reliable way of analyzing clues from a crime scene. Chief Vollmer modernized not only the Los Angeles Police Department but law enforcement in general by introducing the use of: (1) a crime investigation laboratory; (2) a fingerprint and handwriting classification system; (3) a workable system for filing information about the way a crime was committed; and, (4) the creation of a police school where scientists would teach courses in the study of criminal behavior or criminology.

The Bureau of Investigation, renamed the Federal Bureau of Investigation in 1935, continued Vollmer's work in 1932 with the creation of the first national crime lab in Washington, D.C.

Modern forensic investigations

Firearms and toolmark identification

The identification of firearms and weapon-related evidence has played a critical role in crime investigation throughout the twentieth century. Firearms investigations involve the examination of fired bullets to determine what kind of weapon they were fired from. Examinations can eliminate various firearms until a match between bullet and weapon is made. All pistols, revolvers, and rifles contain "rifling" in the bore, the long protruding part through which a bullet travels. Rifling consists of grooves and markings on the inside surface of the bore. These markings have a right or left twist that varies with each manufacturer.

Rifling studies the path of a bullet according to each weapon's bore. A raised marking on the bullet will correspond to a groove in the bore. In addition to rifling characteristics, each fired bullet has tiny imperfections that reflect the imperfections in the bore. A test bullet fired from the gun investigators believe has been used in a crime must be identical to the bullet taken from the crime scene. If the test bullet and evidence bullet have the exact markings, then the crime weapon has been found. Together rifling and imperfections on the bullet can positively identify the weapon used to fire the bullet. These microscopic, or tiny, characteristics are as individualistic as human fingerprints.

Toolmark identification also falls to firearm specialists. Tools such as prying instruments, screwdrivers, and metal bars, or weapons like knives or axes leave identifying marks. Whether on a safe, a door, or a body, toolmarks help identify specific weapons. Tools generally have trace evidence, such as metal shavings, paint, or in the case of a human victim, blood or other biological substances. In assisting the investigation of a crime, both firearms and tool identification add specific information to a body of evidence.

Latent prints

Latent prints refer to fingerprints, palm prints, and the footprints that are not visible to the unaided eye but can be recovered from a crime scene for study. Forensic print specialists retrieve the prints using powders, chemicals, or special lighting. Gathered latent prints are compared against those of suspects, or if no suspects have been identified, they are compared to hundreds of thousands of prints in a computer database.

Fingerprint identification and comparison has been widely used in criminal investigations since the 1920s and early 1930s. A young J. Edgar Hoover (1895–1972), who worked at the Bureau of Investigation, created a fingerprint database in 1924. At that time 810,188 fingerprint records from Leavenworth Penitentiary in Kansas and the National Bureau of Criminal Identification were combined to form the first FBI file.

Questioned Documents

Identifying who wrote a document and the time a document was written depend on analyzing writing characteristics, ink types, and typewriter, printer, and photocopy characteristics. The Questioned Documents department of the crime laboratories also restores documents that are damaged or have faded over time. One major function of document analysis is to determine forgeries, copies or imitation documents created with the intention of pretending they are authentic documents. Log books, letters, diaries, various legal contracts, checks, wills, notes left at a crime scene, and medical records are typical documents that are analyzed. Chemical analysis of ink, including its age, is used to determine changes, additions, or the rewriting of documents.


One of the oldest and largest sections of a forensic crime lab is the chemistry department. The chemistry department undertakes the demanding task of identifying most solids or liquids crime investigators ask them to analyze. Bullet lead, metals from a disaster scene, paint chips from automobiles and structures, dyes, and biological specimens to test for illegal drugs, prescription drugs, alcohol, poisons, and food products all are examples of substances analyzed.

Crime labs generally divide the chemistry department into various parts. Metallurgy units analyze metals for strength, corrosion, or evidence of being tampered with. Paints are analyzed in another unit. Most chemical analyses are preformed on a wide array of instruments that must be maintained and quality controlled to assure accurate results. Maintenance and quality control are carried out by yet another chemistry section. These chemistry sections provide key pieces to crime puzzles.

The toxicology unit, one of the largest chemistry sections, analyzes biological specimens. Toxicology is the study of toxic or poisonous substances, substances that can produce harm or death to any individual who takes them. The toxicity, or deadliness, depends on the amount ingested by the victim. For example, prescription drugs taken as directed do not generally cause a toxic effect, but overdoses of the same drug can lead to death. Toxins or poisons can be manmade or occur naturally in nature like arsenic.

For centuries, poisoning was a favored method of murder, and the study of poisons has gone on just as long. In the twentieth and twenty-first centuries, although poison is still used in a few murders and suicides, accidental poisonings are more common. The American Association of Poison Control Centers states that approximately two million poisoning accidents occur every year.

Trace evidence

Trace evidence refers to microscopic or larger materials, commonly hairs or fibers, which are transferred from person to person or object to object during a crime. Examples include human hair, animal hair, wood fibers, clothing fibers, carpet or car seat fibers, rope, and feathers. Also analyzed in a trace evidence laboratory are dental specimens. Forensic dentistry is known as odontology. Physical anthropologists, who study the physical makeup of humans through millions of years, analyze skeletal remains in the trace evidence lab.


D eoxyribon ucleic a cid, or DNA, is the substance that chromosomes are made of. Chromosomes are long connected double strands of DNA that have a structure resembling a twisted ladder. Along the chromosome strands are genes, or the genetic code unique to every person (except in special cases such as identical twins who have the same genetic code). Individuals inherit one strand of the DNA chromosome from their mother and one strand from their father. The paired chromosomes, one from the mother and one from the father, are located in the nucleus of each individual's cells.

After specific laboratory treatment, DNA double strands separate into single strands. When photographed with the aid of high power microscopes and computers, a single DNA strand appears as a long row of light and dark bands that look something like the bar codes on items for sale. The end result is that scientists can compare two DNA samples to see if the bands line up. If there is an exact match, the two samples came from the same person.

When samples from a crime investigation include blood, saliva, and other body fluids, chromosomal DNA is separated into single strands and the bar code of each strand becomes a DNA profile. If the evidence includes tiny or damaged quantities of DNA from hair, bones, teeth, and body fluids then
another kind of DNA testing can be analyzed and will also produce a unique banded DNA profile.


Explosive experts respond to the scene of an explosion or investigate the discovery of an undetonated (unexploded) bomb. They examine and identify parts of bombs. Even if an explosion occurred, the components used to build and detonate the bomb, although damaged, often can still be identified.

Chemicals, switches, wires, and detonators are all characteristic of the builder. The builder may be an individual or a terrorist group. The number of bomb response units has multiplied across the United States since the bombings in Oklahoma City in 1995 and the World Trade Center Towers in New York City in 1993. The FBI estimates that 85 percent of terrorist activities attempted toward U.S. citizens or interests at the beginning of the twenty-first century involved explosive devices.

FBI crime laboratory

The Federal Bureau of Investigation Laboratory is the most advanced and comprehensive crime laboratory in the world. Not only does it provide scientific evaluations of evidence for U.S. law enforcement agencies, but it also cooperates in sharing information worldwide. The FBI is a federal government agency under the U.S. Department of Justice.

The FBI Lab is made up of twenty-five departments called units organized in two branches, the Forensic Analysis Branch and the Operational Support Branch. The units serve such functions as forensic analysis, scientific analysis, forensic science support, operational response, and operations support. The FBI Lab includes units for firearms and toolmarks, latent prints, questioned documents, chemistry, trace evidence, DNA, and explosives, as well as a wide array of specialized units needed in the twenty-first century. For example, one unit carries out forensic examinations of hazardous materials —chemical, biological, and nuclear. Another unit sends out bomb and crisis response teams that collect and preserve evidence under the most difficult conditions.

There is also a specialized photography unit in the FBI Lab, and a graphics and design unit that recreates exact or scaled down replicas of crime scenes. The FBI Lab Outreach provides educational and training opportunities for lab staff, FBI special agents, local and state law enforcement agencies, and persons involved with forensic laboratories throughout the country.

Forensic analysis

The Latent Prints Unit has two categories of fingerprint holdings, criminal and civil. The criminal fingerprint file contains print records of about 47 million individuals who have been arrested and charged with a crime. The civil files have about 30.7 million print records. Civil prints are made of all employees of the federal government, all members of the U.S. military, those seeking employment in the banking and stock

market industry, individuals applying for U.S. citizenship, adopting a child, or working or volunteering at a child or senior daycare center.

The purpose of keeping the civil print database is to perform background checks searching for a criminal history. The FBI shows an average annual hit of 900,000 checks—or 900,000 prints each year submitted to the civil databases are identified persons with a criminal history record. Civil submissions also are checked against wanted persons files and a terrorist watch list.

The FBI receives approximately fifty thousand fingerprint submissions every day. It received a total of 17,736,541 submissions in 2003. Some 48 percent of these submissions were civil and 52 percent criminal. In July 1999 the FBI revolutionized its databases with the Integrated Automated Fingerprint Identification System (IAFIS). Previously, all prints arrived on paper fingerprint cards that had to be processed by hand. With the introduction of IAFIS, prints and pictures can be submitted electronically.

The IAFIS allows personnel of the Latent Print Unit to quickly process requests from law enforcement agencies all over the country for criminal background checks of people arrested or to check prints recovered at crime scenes against those on file. Many identifications have been made when law enforcement had no suspects. Other times suspicion can be lifted from innocent people and the real offender captured.

The Questioned Documents Unit also compiles a number of databases that can be crosschecked. These databases include a Fraudulent (bad) Check File, Bank Robbery Note File, Anonymous Letter File (threatening unsigned letters), and even a Shoeprint File. Three units provide laboratory analysis of evidence: Firearms-Toolmarks, Latent Prints, and Questioned Documents. The Firearms-Toolmarks Unit provides extensive firearm and toolmark identifications on weapons and tools used in crimes. They also restore serial numbers that have been altered or filed off of firearms to hinder identification.

Scientific analysis

The newest unit in the FBI Lab is the Chem-Bio Sciences Unit. Chem-Bio was added in 2003 for the forensic examination of hazardous materials. This unit works closely with the U.S. military, analyzing chemical and biological, even nuclear, substances and is developing portable identification systems to be taken to field locations where incidents have occurred.

The Chemistry Unit is one of the largest with secondary sections consisting of General Chemistry, Toxicology, Paints, Metallurgy, Elemental (analysis of elements such as lead, arsenic, and silicon in glass), and Instrumentation Operation and Support. The Paint Unit has samples of every color of paint used on U.S. automobiles dating back to the 1920s. Every auto manufacturer in the United States must send in paint samples every year. Most foreign manufacturers also submit samples. From tiny smudges of paint the FBI paint sleuths can identify the make, model, and year of any automobile.

DNA profile matches and checks identify murderers and sex offenders often when there had been no suspect. They also release innocent persons from suspicion. The three DNA divisions are the CODIS Unit, DNA Analysis Unit I, and DNA Analysis Unit II. CODIS stands for Combined DNA Index System. The several CODIS indexes provide (1) a database of DNA profiles from crime scene investigations, (2) a database of DNA profiles of persons convicted of felony sex and other crimes, and later added, (3) a missing persons DNA profile database.

Federal, state, and local forensic laboratories exchange DNA profiles of convicted offenders using CODIS's National DNA Index System (NDIS). The NDIS contained 1,566,552 DNA profiles of convicted offenders as of October 2003. DNA Analysis Unit I (nuclear DNA) and DNA Analysis Unit II (mitochondrial DNA) analyze samples from body fluids such as blood, saliva, semen, and from hair, bones, and teeth.

Forensic science support

The Counterterrorism and Forensic Science Research Unit carries out research activities for all units of the FBI Lab, introducing new and more precise scientific techniques. The constantly evolving methods of this unit help solve crimes and thwart terrorist actions.

The Special Photographic Unit provides a wide range of services such as crime scene photography, surveillance, photography from the air, and aerial mapping. The unit works with traditional photographic processes as well as with digital imaging. In addition, it provides maintenance for photographic equipment throughout the FBI Lab and supports personnel with ongoing training classes.

Operational response

Three units provide some of the FBI's most dramatic services: Bomb Data Center, the Evidence Response Unit, and the Hazardous Materials Response Unit. The Bomb Data Center provides the latest training, techniques, and equipment to local law enforcement bomb squads—those who are the first to respond to threats of explosive and biological weapons.

The Evidence Response Team Unit organizes the activities of Evidence Response Teams (ERTs), made up of FBI special agents trained in evidence recovery from incident sites. ERTs traveled halfway across the world to Piyadh, Saudi Arabia, after vehicle bombs destroyed residential buildings there on May 12, 2003. Twenty-three people, including nine Americans, died in those bombings. ERTs are available to assist foreign

countries when specially requested. ERTs carry out crime scene investigations including evidence collection, the preservation and documentation of that evidence, and also provide photography and fingerprinting.

The Hazardous Materials Response Unit coordinates specialized response teams trained to handle chemical, biological, radiological (radioactive), and nuclear substances. It also oversees national and international training to respond to such materials, and supports FBI response programs located throughout the country. The unit also deals with an increasing caseload of environmental crimes such as the illegal dumping of waste into the nation's waterways.

Operational support

Two units that provide operational support develop fascinating recreations of crime scenes by reconstructing not only buildings, but providing drawings of suspected individuals. The Investigative and Prosecutive Graphics Unit surveys crime scenes, then produces computerized animated scenarios of human movements and actions during a crime. They provide maps, floor plans, diagrams, and timelines, and they are the unit responsible for composite drawings of suspects from victim interviews. The unit can also reconstruct the appearance of individuals from skeletal remains.

The Structural Design Unit supports expert testimony in trials by providing three-dimensional models of crime sites, scale models of vehicles, and models of bomb devices. This unit also provides mannequins of victims for wound locations.

Examples of investigative aids from the Structural Design and Graphics units include the composite drawing of Timothy McVeigh, who bombed the Murrah Federal Building in Oklahoma City; a model of the Murrah Building before and after the bomb blast; a map of Columbine High School in Littleton, Colorado, site of a mass shooting in April 1999; and a model of the cabin where Ted Kaczynski, the notorious "Unabomber," lived in Montana. Until captured Kaczynski mailed sixteen bombs between 1978 and 1995 to selected individuals across the United States killing three and injuring twenty-nine.

Engineering Research Facility

In response to rapidly advancing computer and telecommunications technology, the FBI separated the Forensic Audio, Video, and Image Analysis Unit and the Computer Analysis and Response Team into a new division called the Engineering Research Facility in 2002. The new division is the FBI's cornerstone for counterterrorism and cyber crime (crimes committed by computer, involving the Internet).

The Computer Analysis and Response Team trains and assigns computer specialists to FBI field offices throughout the country. These specialists focus on searching and gathering computer data evidence. The Forensic, Audio, Video, and Image Analysis Unit examines audio, video, and photographic evidence to help solve and prevent crimes.

Sniper attacks

In October 2002 two individuals carried out sniper attacks in the Washington, D.C., area as well as in Virginia and Maryland. Millions of residents were gripped by fear, worrying that their community would be the next to suffer a deadly sniper attack. The offenders were seventeen-year-old Lee Boyd Malvo and forty-one-year-old John Allen Muhammad.

Between the time Malvo and Muhammad were first identified as the offenders and the conclusion of their trials at the end of 2003, six FBI Lab units cooperated to bring the criminals to justice. The units involved were Latent Prints, DNA Analysis, Trace Evidence, Questioned Documents, Structural Design, and Investigative and Prosecutive Graphics.

Solving Old Mysteries

John Wilkes Booth (1838–1865) assassinated U.S. president Abraham Lincoln (1809–1865; served 1861–65) at Ford's Theatre in Washington, D.C., in April 1864. Booth dropped his gun, a single-shot pistol, as he leapt onto the stage and escaped out the back of the theatre. The pistol was put on display in 1940 at the theatre's museum.

In 1997, following the death of a suspected thief, records were discovered that he had stolen Booth's pistol in the 1960s and replaced it with a fake. The U.S. National Park Service, which runs the Ford Theatre Museum, asked the FBI to determine if the museum's pistol was real. Using a photo of the original pistol taken prior to 1960 and the pistol on display, the FBI's Firearms-Toolmarks Unit and the lab's Special Photographic Unit analyzed the pistol itself, the photograph of the pistol, and historic photographs of other pistols of this type.

The lab compared the museum's pistol to other pistols of the same time period and used a dental material to make a cast of the inside of the gun barrel. The FBI determined that the pistol had a number of unique markings and characteristics including a crack in the wooden part of the gun. These characteristics confirmed the pistol that was in the museum was from the time period of Lincoln's assassination, was not a replica made in later years, and was the actual gun that had killed the president.

Around October 23, 2002, the police department of Montgomery, Alabama, decided to submit fingerprints gathered from the murder of a convenience store clerk to the FBI Latent Print Unit. They suspected whoever carried out the shooting

spree in the Washington, D.C., area might be the same individuals involved in the convenience store murder. FBI personnel entered the fingerprints into the Integrated Automated Fingerprint Identification System (IAFIS) and got a match. The prints belonged to Malvo, who had once been arrested on an immigration violation. Further examination of Malvo's records found another name—John Allen Muhammad. The Latent Print Unit matched Malvo's and Muhammad's fingerprints to items left at the crime scenes. Twelve hours later Malvo and Muhammad were apprehended at a highway rest stop in Maryland.

The FBI's DNA units matched DNA from the crime scenes and from the car of the snipers. The samples matched Malvo and Muhammad and included such evidence as bags, notes, a brown glove, and hairs found in a duffel bag and on a coat from crime scenes, as well as the weapons recovered from the car.

The Trace Evidence Unit matched blue, gray, and white fabric fibers to the car seats of the snipers. Trace Evidence also found brown fibers collected at the crime scenes matching brown gloves, one of which was left at a crime scene, the other one from the car. Questioned Documents analyzed notes written and left at two crime scenes and determined that they were written by the same person who wrote in a manual found in the suspects' car.

Both the Structural Design and Graphics units provided visual reconstructions used as exhibits in trials. Structural Design built a full-sized replica of the snipers' trunk, complete with the specially made hole from which shots could be fired. Graphics produced digital images of the white van and truck originally thought to belong to the suspects; made diagrams of crime sites, their victims, and possible positions of the shooters; and provided a timeline of the sniper attacks.

Both Malvo and Muhammad were found guilty of carrying out the sniper attacks. Malvo, largely because of his young age, received life in prison without parole. Muhammad was sentenced to death.

The FBI Lab units played a major role in the arrest and conviction of Malvo and Muhammad. Many criminal cases, like the D.C. sniper case, involve the cooperation of many departments and units on local, state, and federal levels. They all have the same goal of collecting, preserving, and analyzing all kinds of evidence to bring criminals to justice.

For More Information


Federal Bureau of Investigation. FBI Laboratory 2003. Quantico, VA: U.S. Department of Justice, 2003.

Inman, David, and Norah Rudin. Introduction to Forensic DNA Analysis. Sarasota, FL: CRC Press, 1997.

Lane, Brian. Crime and Detection. New York: Alfred A. Knopf, 1998.

Smyth, Frank. Cause of Death: The Story of Forensic Science. New York: Van Nostrand Reinhold Company, 1980.

Web Sites

American Association of Poison Control Centers. (accessed on August 19, 2004).

Federal Bureau of Investigation (FBI). (accessed on August 19, 2004).

Human Genome Study Information. (accessed on August 19, 2004).