Evidence Collection & Preservation Flashcards

At a scene where multiple firearms were discharged, how should investigators differentiate cartridge casings from different weapons?

Answer: By caliber, headstamp, case type, and ejector/extractor marks examined at the lab

Laboratory examination of caliber, headstamp, and microscopic toolmarks from ejectors and extractors links specific casings to specific firearms.

An agent must collect a blood sample from a suspect vehicle seat. Which collection method is most appropriate for a dried bloodstain?

Answer: Swabbing with a dry swab followed by a moistened swab

The dry-wet swab technique — first a dry swab to collect surface particles, then a moistened swab to rehydrate and collect remaining material — maximizes DNA yield from dried stains.

What is the purpose of using a metal detector grid search at an outdoor shooting scene?

Answer: To systematically locate all metallic evidence including casings and bullet fragments

A systematic grid search with a metal detector ensures comprehensive recovery of all metallic evidence across the scene without missing items.

A defense attorney claims evidence was contaminated because an agent used the same gloves to handle multiple items. What principle does this violate?

Answer: Cross-contamination prevention protocols requiring glove changes between items

Agents must change gloves between handling different evidence items to prevent cross-contamination that could compromise forensic results and court admissibility.

In a shooting scene involving a through-and-through bullet, what term describes the mark left on the far side of a struck surface?

Answer: Exit defect

An exit defect is the mark or hole on the far side of a struck surface where the bullet emerged, typically larger and more irregular than the entry defect.

What is the significance of the 'chain of custody' documentation in shooting evidence cases?

Answer: It establishes unbroken accountability for evidence from collection through court presentation

Chain of custody documents every person who handled evidence and when, establishing unbroken accountability required for evidence admissibility in court.

When packaging multiple items of evidence from the same scene, why must each item be packaged separately?

Answer: To prevent cross-contamination and maintain individual item integrity

Individual packaging prevents trace evidence from one item contaminating another, which could create false associations or destroy legitimate forensic links.