Be a little careful.. it sounds like you know quite a bit about this guy (which is....interesting)... like it was said before this person will probably not "come after you"... but DON'T tell anyone about this including local LE... and insist on being anonymous with the FBI, if he is a mental case you never know what could possibly happen to you or your family, speculating one way or the other is nice... but if something happens all bets are off. If this guy had the balls to vandalize someone's airplane... you can only imagine what could possibly happen to you/your stuff.
Bottom line.. don't be an idiot about this thing... give the FBI the info and keep your mouth shut as much as possible. Since you know so much about this person it is possible, this person knows a bit about you.