Criminal Investigations and Evidence Handling
This domain tests lawful collection, preservation, and documentation of evidence, plus investigative procedures that survive suppression and trial challenges.
Core rules
- Photograph evidence in place before moving it, then collect with gloves, package each item separately, and label with date, time, location, collector, and case number.
- Maintain an unbroken chain of custody from collection through storage, analysis, and court. Every transfer should be documented. A gap affects weight, not automatic admissibility.
- Biological evidence must be air-dried before packaging; airtight plastic can promote degradation and mold. Digital evidence must be preserved without altering metadata, preferably by forensic copy and hash value.
- Search-warrant affidavits need probable cause, particularity, and a nexus between the place to be searched and the evidence sought. Stale information may not support probable cause.
- Custodial interrogation requires Miranda. Voluntariness requires no threats, promises, or coercive tactics. Eyewitness identification should use unbiased procedures, such as double-blind sequential lineups, and document the witness's confidence statement.
- Document every investigative step that may affect admissibility, including who handled evidence and when.
Worked example
A burglary victim reports a pry bar in the yard. The officer photographs the pry bar where it lies, collects it with gloves, and packages it. The officer labels the package and books it into evidence the same shift. At the lab, each transfer is recorded. At trial, the defense shows the officer left the pry bar in a patrol car for six hours before booking. The chain is not broken, but the gap is a weakness. The evidence may still be admitted if authenticated, but the jury may give it less weight. The officer should have booked it immediately.
Traps that cost marks
- Assuming a chain-of-custody gap automatically excludes evidence.
- Packaging wet biological evidence in plastic.
- Writing a warrant affidavit that lacks a nexus to the place searched.
- Failing to document witness identification procedures and confidence statements.