U.S. Fish & Wildlife Service
Forensics Laboratory

Forensics Lab Home
Science Professionals
Agents and Insectors
Students and Educators
Publications and ID Notes
The Feather Atlas
Lab Tour
Lab News
About Us
Contact Us
Site Map

Indian Peafowl Feathers. Credit: USFWS

Students and Educators


  • What forensic scientists really do with evidence
  • The definition of chain of custody
  • The definition of an expert witness
  • The greatest difficulty facing a crime scene investigator
  • That truly fictional character

What Forensic Scientists Really Do with Evidence …

  • They examine and identify evidence based on the class characteristics of the evidence items
  • In a triangular fashion, they attempt to link the suspect, the victim and the crime scene using the individual characteristics of the evidence items

Hopefully, it goes without saying that a suspect should never be positively linked to a victim or a crime scene based only on class characteristics of evidence.

The Definition of Chain of Custody …

If you have the opportunity to alter, switch or destroy an item of evidence without detection, then you are, by definition, in the ‘chain of custody’ of that evidence item.
That means, among many other things, that you could be subpoenaed to testify that you did not alter, switch or destroy that evidence item

The Definition of an Expert Witness …

  • An expert witness is an individual who has “more knowledge or expertise on a subject than the common man/woman”
  • An expert witness is allowed to offer opinion testimony to the courts
  • All other witnesses (including, in theory, the suspect) can only offer factual
    testimony to the courts
That Truly Fictional Character
That Truly Fictional Character. Credit: Illustrated by Bob Dawson © Kenneth Goddard

The Greatest Difficulty facing a Crime Scene Investigator …
They usually have little or no idea what the scene was like before the suspect and victim interacted … thus the need to carefully evaluate the scene and the evidence!

And finally …

That Truly Fictional Character … a ‘generalist’ criminalist (forensic scientist) who is capable of performing any and all functions within a crime lab.


U.S. Department of Interior Logo