Forensic experts, also called criminalists, use the instruments of science and engineering to examine physical evidence. They use spectroscopes, microscopes, gas chromatographs, infrared and ultraviolet light, microphotography, and other lab measuring and testing equipment to analyze fibers, fabric, dust, soils, paint chips, glass fragments, fire accelerants, paper and ink, and other substances in order to identify their composition and origin. They analyze poisons, drugs, and other substances found in bodies by examining tissue samples, stomach contents, and blood samples. They analyze and classify blood, blood alcohol, semen, hair, fingernails, teeth, human and animal bones and tissue, and other biological specimens. Using samples of the DNA in these materials, they can match a person to a sample of body tissue. They study documents to determine whether they are forged or genuine. They also examine the physical properties of firearms, bullets, and explosives.
At the scene of a crime (whether actual or suspected), forensic experts collect and label evidence. This painstaking task may involve searching for spent bullets or bits of an exploded bomb and other objects scattered by an explosion. They might look for footprints, fingerprints, and tire tracks, which must be recorded or preserved by plaster casting before they are wiped out. Since crime scenes must eventually be cleaned up, forensic experts take notes, photographs, and video to preserve the arrangement of objects, bodies, and debris. They are sometimes called on later to reconstruct the scene of a crime by making a floor plan or map pinpointing the exact location of bodies, weapons, and furniture.
One important discipline within forensic science is identification. Fingerprint classifiers catalog and compare fingerprints of suspected criminals with records to determine if the people who left the fingerprints at the scene of a crime were involved in previous crimes. They often try to match the fingerprints of unknown corpses with fingerprint records to establish their identities. They work in laboratories and offices, and travel to other areas such as crime scenes. Retrieving fingerprints outside may be difficult and require specialized processes, such as dusting glassware, windows, or walls with a fine powder. This powder contrasts with many different surfaces and will highlight any fingerprints that remain. Another method of retrieving fingerprints is to lift them off with a flexible tape, which can be brought back to the laboratory for further evaluation and matching.
Fingerprint classifiers compare new prints against those found after the commission of similar crimes. The classifier documents this information and transfers it to the main record-keeping system, often a large mainframe computer system. In the last two decades or so, computers have greatly enhanced the possibility of matching new fingerprints to those already on file. A fingerprint classifier may keep individual files on current crimes and note any similarities between them.
Identification technicians work at various jobs related to maintaining police records. In addition to handling fingerprint records, they also work with other kinds of records, such as police reports and eyewitness information about crimes and accidents. They operate equipment used to microfilm police records (or work with databases that store digital copies of records), as well as store the microfilm and retrieve or copy records upon the request of police or other public officials. Forensic pathologists perform autopsies to determine the cause of death; autopsies are almost always performed on victims whose deaths are linked to crime.
Forensic experts work in a wide range of additional specialties.
Computer forensics specialists examine computers and other technology for evidence of wrongdoing. They may also be known as computer or cyber examiners.
Forensic anthropologists examine and identify bones and skeletal remains for the purposes of homicide, scientific, archaeological, or judicial investigations.
CrimeMuseum.org defines ballistics as the “study of motion, dynamics, angular movement, and effects of projectile units (bullets, missiles, and bombs).” Forensic ballistics and firearms investigators study guns (handguns, rifles, machine guns, etc.) and the bullets that they fire. Every time a gun is fired, unique microscopic marks are made on the surfaces of bullets and cartridge cases. When a crime occurs, these experts analyze these marks to connect cartridge cases and bullets to suspected criminals.
Forensic biologists employ scientific principles and methods to analyze biological specimens so they can be used as evidence in a court of law. Forensic botanists collect and analyze plant material found at crime scenes.
Forensic chemists conduct tests on evidence from crime scenes, such as paint chips, hair, fire debris, or glass fragments, either to identify unknown substances or to match the evidence against materials found on potential suspects.
Forensic engineers are specialized engineers who study materials, devices, structures, and products that do not work as they were designed to or fail to work completely. They also provide written or oral testimony regarding their findings or educated opinions in legal proceedings.
Forensic entomologists use insect-related evidence and their knowledge of insects to provide facts for civil and criminal cases. They are sometimes referred to as medical entomologists or medicocriminal entomologists in criminal investigations.
Forensic nurses are trained to work with victims, suspects, and evidence of crimes, and work in a variety of settings.
Forensic odontologists use dental records and evidence to identify crime victims and to investigate bite marks.
Forensic psychiatrists conduct psychiatric evaluations of accused criminals and are often called to testify on whether the accused is mentally fit to stand trial.
Forensic toxicologists detect and identify the presence of poisons or legal or illegal drugs in an individual’s body.
Molecular biologists and geneticists analyze and review forensic and paternity samples, provide expert testimony in civil and criminal trials, and identify and develop new technologies for use in human identification.
Forensic experts spend the bulk of their time in the laboratory working with physical evidence. Except for forensic psychiatrists, they seldom have direct contact with persons involved in actual or suspected crimes or with police investigators except when collecting evidence and reporting findings. Forensic experts do not interpret their findings relative to the criminal investigation in which they are involved; that is the work of police investigators. The purpose of crime lab work is to provide reliable scientific analysis of evidence that can then be used in criminal investigations and, if needed later, in court proceedings.
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