My running theory is that this was a "protest suicide" intending to rile people up. Sort of like the "burning yourself to death on the capital steps" kind of thing.
He had the knowledge and skills to do a lot of damage and chose instead to do something loud and showy and kill himself without injuring anyone else.
I doubt we will ever know though. If there is some sort of note/manifesto like these people love so much it will be hidden from the public for 200 years.