Without a Trace? Advances in Detecting Trace Evidence

National Institute of Justice

   See also the instructional videos on "Evidence Collection"

Shards of glass are found at the scene of a hit and run. It’s the same type of glass used to make most standard headlights.

A single hair might belong to a missing woman, but it is coated with conditioner, making microscopic analysis impossible. Investigators at the site of a plane crash search for minute quantities of explosives in the wreckage. At the scene of a rape and murder, officers hope to find blood or semen from the assailant.

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Currently, law enforcement has no accurate way to match the glass shards or coated hair to known samples, and locating tiny particles of explosive material or body fluids might be difficult or impossible. But all that’s about to change, as new and improved techniques for detecting and distinguishing trace evidence—minute quantities of materials such as blood, chemicals, fibers, glass, hair, plant material, or plastics—are very close to being added to the law enforcement arsenal.

Connecting a person or object to a specific crime scene is often essential to proving guilt or innocence. Developing such a link is frequently based on identifying and comparing trace evidence. Because trace evidence samples can look similar and the environments where they are found are often complex, identifying unique characteristics and establishing a link can be difficult. Older techniques often cannot distinguish such evidence due to these challenges.

New technologies for trace evidence may help eliminate many of these obstacles, allowing more trace evidence to be found and identified. Here are four of the most promising new techniques.

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