Name Date
Forensic Science Lab: Locard’s Principle of Exchange
Background: A fundamental principle of investigation for every crime scene comes from
Edmond Locard, a forensic investigator in the early 1900s. It was Locard's belief that when a
criminal came in contact with an object or person, a cross-transfer of evidence occurred.
Locard strongly believed that every criminal is connected to a crime by trace evidence carried
from the crime scene.
In this lab, you will examine an article of “clothing” recovered from the apartment of a
suspect in the rape & murder of a 32-year old woman whose body was found by investigators
in a park 5 blocks from the suspect’s home. Witnesses observed the victim escorting the
suspect into her home after attending a baseball game approximately 3 hours before her body
was discovered. The victim lived alone & was often seen by neighbors walking her dog in the
early mornings & late afternoons.
When investigators performed the search on the suspect’s apartment that yielded the
suspicious article of clothing, it was observed to be clean, pet-free, & smelled faintly of
cigarette smoke. Further investigation revealed that the suspect worked as a mechanic at a
local auto-repair shop.
Procedure
1) Each group will receive a cloth representing an article of clothing recovered by
investigators from the suspect’s apartment that he allegedly wore the night of the
murder.
2) The numbered items on the cloth represent debris that must be examined
microscopically. Collect these debris items from the cloth article by lifting it with
transparent tape –lightly touch the tape to the cloth & apply it to a clean microscope
slide. A single slide should be made for each debris type found on the cloth.
3) Examine each slide under the microscope.
4) In the table below, attempt to identify each of the numbered debris items collected from
the cloth after examining it under the microscope.
5) Use the pictures at the end of the lab illustrating the appearance of common materials
under the microscope to help you identify each debris type.
Debris Recovered from Clothing Article
(1)
(2)
(3)
