How Crime Scene Investigation Works


Analyzing the Evidence: Forensic Science

­The first forensics lab in the United States opene­d in 1923 in Los Angeles. In 1932, the FBI established its own forensics lab to serve police departments and other investigating authorities all over the country. The FBI lab is one of the largest in the world.

The Denver Crime Lab at the Colorado Bureau of Investigation provides evidence collection and laboratory analysis for any police department in Colorado that requests its services. It also conducts state investigations that don't fall under the jurisdiction of any local authority.

Some specialty departments in the Denver Crime Lab include latent fingerprints and impressions, which develops latent fingerprints; analyzes and compares fingerprints, footwear and tire impressions; and runs fingerprints through the Automated Fingerprint Identification System (AFIS, which uses the FBI database) for comparison against hundreds of millions of prints.

CBI technicians use these camera setups to photograph recovered prints to use in comparison and for running through the AFIS system. On the left is an old-school Polaroid setup, and on the right is a digital-camera setup. Mr. Clayton prefers the Polaroid results.

The trace evidence department runs GSR analysis, and identifies and compares samples of soil, glass, fibers and paint. The chemistry section conducts analysis and comparison of illicit drugs, explosives and unknown chemicals. The computer crimes team recovers evidence from computers and performs computer enhancement on audio or video evidence. There's also firearms and toolmark identification, which identifies firearms; tests firearms to establish barrel pattern and distance of gun from entrance wound; and identifies and compares bullets, casings and toolmark impressions. Then there's serology and DNA, which conducts body fluid analysis, including DNA analysis for blood stains, semen and hair for identification and comparison.

Comparison microscope setup in the CBI serology lab

Lastly, there's a questioned document section that detects forgery and alterations; conducts handwriting comparisons; reconstructs destroyed documents; and identifies and compares printers, typewriters or copiers used to produce a document.

Often, a piece of evidence passes through more than one department for analysis. Each department delivers a complete report of the evidence it analyzed for the case, including the actual results (numbers, measurements, chemical contents) and any expert conclusions the scientists have drawn from these results. The CSI in charge might compile the results and deliver them to the lead detective on the case, or the lab might send the results directly to the detective squad.

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