My opinion, he was just a lunatic mass murder for years, just waiting to be set free and maim and kill.  There are always a few of these psychos around, keeping it hidden, either sad or happy, and captain of the wrestling team, both brothers in pugilistic sports, that's kind of a tell,but there are no tells, no way of knowing which regular guy or sad sack has horrendous demons straining to break free.  I always thought the Hannibal lector version of what makes these fiends tick is pretty much the simple truth.