Investigative techniques, surveillance, interviews, and evidence handling
Surveillance and interviews
Plan before acting: identify the legal authority, objective, subject profile, location, contingencies, and documentation method. Static and mobile surveillance require cover, lawful positioning, and accurate records of time, date, and place. Photograph and video with metadata preserved. For interviews, identify yourself truthfully unless a lawful pretext is appropriate, explain the purpose, use open-ended questions, listen actively, and avoid leading or contaminating witnesses. Separate witnesses before interviewing them. A cognitive interview approach can improve recall without suggestion.
Evidence handling
Preserve original digital files and avoid editing them. Use hash values where appropriate. Label and photograph physical evidence, document the chain of custody, and log every transfer. Reports should be chronological and factual, distinguishing personal observation from statements made by others. Do not state conclusions beyond your expertise.
Worked example
A witness says, I think he left around nine. The report should say the witness estimated nine o'clock, not the subject left at nine. Corroborate with video, receipts, or time records. Writing the latter creates false certainty and gives opposing counsel an impeachment point.
Traps
Leading questions and failing to separate witnesses can contaminate a case. Not documenting time and place weakens the work. Editing original files or failing to log transfers breaks authentication. Trespassing during surveillance or recording illegally can destroy an otherwise strong investigation.