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.
Then as Sherlock Holmes said, "I am not retained by the police to make up for their deficiencies." ("The Adventure of the Blue Carbuncle")
What you’re saying is that anyone in the right position could have discovered the information but You do not know if any else did.
Personally I wouldn’t grieve over this mans death. You saved a lot of people from suffering unnecessarily.