He was an extremely paranoid man dedicated to privacy so much that he built these retarded fences around his mansion that ruined the neighborhood.
He saw an opportunity to take revenge against society for destroying his brother who got caught for CP, I think? He probably was under investigation for a while, too. He lived a really extreme life full of gambling and shit. It’s not that farfetched that he did a bunch of illegal shit.
Probably the FBI was onto him for something and gave up. Then they covered that part up when he did the thing because it made them look bad.