Investigations and Evidence Handling
Investigations and Evidence Handling
This domain tests whether your case survives a motion to suppress and a trial: scene control, documentation, chain of custody, identification, and follow-up.
Scene and evidence
- Locard's exchange principle - every contact leaves a trace. Protect the scene, log who enters, and start the crime scene log before anything is moved.
- Chain of custody - every transfer, date, time, and signature. A gap is an opening for the defense.
- Package biological evidence in paper and air-dry wet items; sealed plastic grows mold and destroys DNA. Package each item separately to prevent cross-contamination.
- Document before you collect: photographs, sketches, measurements, and a written description of the item where it lay.
Identification and statements
- Showups need probable cause and should occur near the scene and soon after the crime; photo arrays follow a blinded, sequential protocol to reduce suggestibility.
- Record statements verbatim where possible; note Miranda, the time, and who was present. A spontaneous utterance is strong evidence; a later summary is weak.
Court process
- Search warrant affidavits need particularity and probable cause; the return and inventory must be filed.
- Laboratory certificates are testimonial under Melendez-Diaz v. Massachusetts; the analyst must appear.
Worked example
A burglary yields a bloodstain on a broken window and a latent print on the sill. Correct handling: photograph both in place, swab and air-dry the blood into paper packaging, lift the print onto its card, log each transfer, and submit them separately. Bagging them together destroys the chain, and the defense will say so.
Traps
Plastic-bagging wet evidence; skipping the scene log; a one-officer showup weeks after the crime; relying on a lab certificate without the analyst; undocumented follow-up.