Forensic comes from a Latin word meaning “public” or “forum,” and in English, it can mean “used in courts of law.” Forensic science, then, is any field of science as it applies to the law, and a forensic expert witness is a forensic scientist from any field who provides testimony to a court or in court.
A forensic expert witness may be involved in one of any number of areas of scientific pursuit. He or she may be an anthropologist, a biochemist, a chemist, a dentist, a medical examiner, a psychologist, a psychophysiologist, a toxicologist, or an expert in areas such as ballistics, computers, crime scene reconstruction, fingerprints, firearms, explosives, handwriting, textiles, or toolmarks.
A forensic expert witness is often involved in criminal cases from shortly after the crime is discovered. She or he may be present at the crime scene and involved in examining and collecting physical evidence from the site, using appropriate kits for biological evidence and footprints, collecting impressions of fingerprints, and gathering specimens of other pertinent evidence. Documenting the scene with written records and photographs is another aspect of the job.
The forensic scientist’s role often includes work in a laboratory, examining and analyzing evidence with tools and techniques specific to his or her specialty. Depending on that specialty, the forensic scientist may use certain tools that are standard in many laboratories. Examples include tools such as chromatographs, spectrographs, and scanning electron microscopes, depending on whether the scientist is, for example, analyzing drugs, chemicals, or comparing very small amounts of questionable material with known material, respectively.
There are also tasks that are more particular to forensic science. Often, this may involve analysis done with or through software or database interfaces. For example, when seeking to match unidentified DNA found at a crime scene, the forensic scientist might tap into resources such as DNA sequence analysis software and the Combined DNA Index System (CODIS). When seeking to establish the identity of crime scene fingerprints, fingerprint identification systems, such as Automated Biometric Identification System (ABIS) or Integrated Automated Fingerprint Identification System (IAFIS) may be used.
Both the prosecution and the defense in criminal trials and both the defendant and the plaintiff in civil trials may call for forensic expert witness testimony. Findings or opinions of forensic expert witnesses may either be presented as reports, or they may be asked to appear in court. There is special training available for forensic scientists who are going to be asked to make court appearances.