I see it this way. Did you come across the knowledge of how to prevent this mans death suddenly or was it gained over a period of time. Whatever your ‘proof’ was, was it undeniably truthful. If you had spoken out, would it have involved a situation where someone could have committed perjury and created doubt your statements were false?
Did you learn about this ‘proof’ in a manner that leaves you to think that you were suppose to share it rather than conceal it? Do you think anyone else had the same ‘proof’ that you did and they withheld it also?
I came across this knowledge abruptly, during the course of my duties at the time. The proof was unassailable and ALL of it was discover-able independently of me. It is just that no one else knew where or what to look for.