Even if the guy was not guilty, he may have been something of a whackjob. I wonder if he is going to be sainted by some here on FR, as some other previous whackjobs have been.
It does appear to be quite possible that he lost it towards the end of his life, but that COULD very well be because he was going to be officially charged with being a mass murderer when he wasn't, which I suspect would push a lot of people over the edge.
But as a general rule, it's extremely difficult for a true "whackjob" to be cleared for decades to work in a place such as the USAMRIID at Ft. Detrick. If he was nuts, he did an amazing job of hiding it from his family, friends, co-workers, and the government which gave him the Decoration for Exceptional Civilian Service.
Some people who worked closely with him have already gone on record as saying that they think this whole thing is a bunch of bunk.