Investigative Techniques and Evidence Handling
Plan, then document
Open every case with a written plan: the question to be answered, lawful methods, budget, and reporting deadline. Then document contemporaneously. Notes recording times, locations, and sources at the moment carry far more weight on the stand than a report reconstructed a week later.
Surveillance boundaries
Observation from a public place, such as a street, sidewalk, or parking lot, is generally lawful. Crossing onto private property, peering into residence windows, or blocking a subject's movement is not; ORS 164.245 covers criminal trespass. Keep a safe distance, obey traffic law, and break off when the subject's behavior shows you have been made.
Chain of custody
For physical items, record who obtained the item, when, where, from whom, and every transfer afterward. Store it in a sealed, labeled container and log each opening. For digital evidence, preserve the original, compute and record a hash value, work from copies, and document every access. Testimony about a file you cannot show was unaltered is easily excluded.
Admissibility basics
Under the Oregon Evidence Code, physical and digital evidence must be authenticated under OEC 901 by a witness who can explain what the item is and that it is what it purports to be. Business records are admitted under OEC 803(6) when shown to have been made in the regular course of business at or near the time of the event.
Worked example
A witness hands you a phone containing relevant texts. Do not scroll through it, screenshot selectively, or delete anything. Photograph the phone as received, note the time and the witness's identity, keep it sealed, and return it to the owner or deliver it to law enforcement or counsel with a written receipt.
Traps that cost marks
Altering or cleaning up original files; summarizing instead of quoting; losing the chain when a colleague takes over; confusing relevance with admissibility; trespassing to get a better camera angle.