Investigations and Evidence Handling
Domain focus
This section tests case management from first response through prosecution: scene control, evidence integrity, interviews, documentation, and discovery obligations.
Core rules and concepts
- The first responder secures the scene, preserves life, isolates witnesses, protects the scene, and records the initial condition. Contamination is easier to prevent than to explain.
- Chain of custody must show who had the item, when, and where from seizure through analysis and court. Gaps create challenges to admissibility and weight.
- Package evidence by type: dry biological evidence in paper, wet items allowed to air-dry, drugs and weapons secured and labeled, digital evidence preserved without altering metadata.
- Interviews should be separate, documented, and non-leading. Record custodial interrogations when practicable and preserve notes.
- Massachusetts discovery obligations require production of relevant materials; exculpatory evidence must be disclosed under Brady. Failure can lead to sanctions or reversal.
Worked example
A burglary scene yields a latent print, a bloody glove, and video from a nearby camera. The lieutenant should assign scene security, photograph the glove before collection, package it in paper after drying, log the print and video, and record every transfer. The video should be copied with a hash value and the original preserved. Reasoning: biological evidence in plastic can degrade; unbroken documentation and authenticated copies make the evidence usable at trial.
Traps that cost marks
- Packaging wet biological evidence in plastic.
- Letting officers handle evidence without logging the transfer.
- Interviewing witnesses together and creating memory contamination.
- Viewing digital evidence on the original device and changing metadata.
- Failing to document negative findings and scene changes.