True-crime research often places a police record, sworn testimony, newspaper story, documentary, forum post, and decades-later memory on the same screen. They are not the same type of evidence.
Primary does not mean perfect
A primary source was created close to the event or by a participant: an original letter, report, photograph, recording, court filing, or contemporaneous note. It can still contain mistakes, omissions, bias, or an incomplete perspective. Record its creator, date, purpose, and chain of custody where known.
Testimony needs context
Testimony may be sworn or unsworn, contemporaneous or much later. Identify when the statement was made, what question prompted it, whether it changed, and whether another record supports or contradicts it. Do not turn a person’s statement into an established fact without qualification.
Later retellings can help—and distort
Books, documentaries, articles, and websites can organize a large record and point readers to sources. They can also repeat one another until an unsupported claim appears settled. Follow footnotes and links back as far as possible. If every retelling traces to the same unverified statement, the number of repetitions does not create independent confirmation.
Use a simple source label
For each important claim, record:
- what is being claimed;
- the earliest located source;
- source type and date;
- direct quotation or faithful summary;
- corroborating or conflicting material; and
- what remains unknown.
Zodiac Killer X should use this method across facts, testimony, timeline, and case files. Case research is stronger when readers can inspect the source path and see uncertainty—not when a dramatic conclusion outruns the record.