Begin with the decision
A useful investigation starts with the decision someone must make. Naming that decision prevents activity from becoming the objective and helps define what level of confidence is actually required.
Separate what is known from what is assumed
List direct observations, reliable records, reported information, and working assumptions separately. This exposes contradictions early and prevents an inherited narrative from becoming the conclusion.
Write the unresolved questions
Unknowns should be specific enough that an observation, record, interview, or other lawful source could change the answer. Broad questions produce broad collection and weak conclusions.
Confirm authority and constraints
Record who is requesting the work, their relationship to the matter, the lawful purpose, relevant jurisdiction, time limits, safety concerns, privacy limits, and any restrictions on method or disclosure.
Define a useful stopping point
The goal is not perfect information. The work should stop when the evidence is sufficient for the decision, the remaining uncertainty is explicit, and further collection would not justify its cost or intrusion.