Criminalist Pete Evett is collecting fiber evidence from a murder scene. He notices fibers on the victim's shirt and trousers, so he places both of these items of clothing in a plastic bag. He also sees fibers on a sheet near the victim, so he balls up the sheet and places it in a separate plastic bag. Noticing fibers adhering to the window sill from which the attacker gained entrance, Pete carefully removes them with his fingers and places them in a regular envelope. What mistakes, if any, did Pete make while collecting this evidence?
Sample Answer
Criminalist Pete Evett made several critical errors in his collection process. In forensic science, the integrity of fiber evidence depends entirely on preventing cross-contamination and avoiding the loss of microscopic materials.
Based on standard forensic protocols, here are the mistakes Pete made:
1. Co-mingling Items in the Same Container
Pete placed both the shirt and the trousers into a single plastic bag.
The Mistake: This is a major error known as cross-contamination. By placing two different items of clothing in one bag, any fibers originally on the shirt could transfer to the trousers and vice versa.
The Consequence: In court, a defense attorney could argue that a "matching" fiber found on the trousers was actually transferred from the shirt during transport, rendering the evidence useless for proving where the suspect made contact. Every item of clothing must be packaged in its own separate container.
2. Using Plastic Bags
Pete used plastic bags for the clothing and the sheet.
The Mistake: Non-porous containers like plastic trap moisture.
The Consequence: If the clothing or sheet has even a trace of moisture (blood, sweat, or dew), the airtight environment of a plastic bag will promote the growth of mold and mildew. This can destroy biological evidence and degrade the physical characteristics of the fibers. Forensic evidence should be placed in paper bags or breathable containers.