But, then he is tainted.

Forever.

I say it is impossible to make a judgment form one-sided story presented in the letter.

The letter writer could have an ax to grind. He calls him "insane", he doesn't say what prompted the remarks that are reported, and the "proofs" of the other employee's insanity and dangerousness don't worry me at all (as reported.)

Though, he does sound a bit like "Dwight" in the office. And maybe he is trying to!

I feel sorry for him.

Until or unless he does or says something more indicative of being dangerous - because there is no problem with being insane as long as he's not dangerous, right?

I think Lucy's advice, to get to know him better, is the best advice. Maybe he is dangerous. But, maybe they just don't get him.