1. Build the timeline first
Write down every time supplied by an independent source: alarms, access records, messages, instruments and witnesses. Do not force them into one sequence too early. A useful online detective game may present several clocks that are accurate in different ways—or one event staged to look like another.
Mark gaps and impossible overlaps. If an explanation requires a person to cross the same corridor twice in one minute, either the explanation is wrong or one of its times describes something different from what you assumed.
2. Label facts, claims and inferences
A visible object is evidence. A witness statement is a claim. Your account of why the object is there is an inference. Keeping those categories separate prevents a confident character from quietly becoming your narrator.
Also ask whether a contradiction concerns the central crime. Someone may lie to hide embarrassment, a policy violation or a private relationship. A lie creates a question; it does not answer every question.
3. Try to disprove your favourite theory
Once you have a suspect or sequence, search for the detail it explains least well. Check access, physical capability, knowledge and motive separately. The strongest theory should account for ordinary facts as well as dramatic clues without inventing extra events.
Dead Orbit turns this method into a free mystery solving game online. After each chapter, the evidence review asks which reconstruction is best supported and which conclusion goes beyond what the pages establish. Submit before seeing the explanation, then carry the corrected model into the next chapter.