How do you check claims that someone was killed for revealing secrets?

Break the story into separate claims. Did the person actually make the statements attributed to them? Is there reliable evidence they had access to the information? What is known about the death, and what specifically connects it to the alleged disclosure? A post can provide strong evidence for one part and little or none for another.

Look for records and reporting that can be checked independently, not just later retellings that cite one another. A dramatic timeline or a claimed motive is a reason to ask questions, not proof of a plot.

Be careful with the word “eliminated.” It turns an uncertain explanation into a conclusion. A death may be documented while the supposed reason for it remains unproven. Timing, enemies, or an unusual circumstance can raise questions, but they do not by themselves establish who caused a death or why.

I'd also compare competing explanations and note what evidence would change the assessment. If a post leaves out uncertainty or treats every gap as evidence of a cover-up, that is a warning sign.

There are two mistakes to avoid: accepting a sensational claim because it sounds alarming, and dismissing every possibility of retaliation out of hand. Keep the conclusion proportional to the evidence. Documented threats or pressure can support a claim of intimidation, but that is different from proving a killing was arranged.

If the evidence is thin, “unverified” is a fair stopping point. You don't have to decide that a story is either definitely true or definitely impossible.