Supposedly he was autistic.
I will make a few guesses.
He was on some psychoactive med, ssri, ritalan, xanax or pot.
He would spend a huge amount of time in the fantasy world of first person shooter video games.
He was addicted to pornography. Probably got that from his dad.
But it's the NRA's fault.
Based on what evidence? The fact that his dad made a few photos of female derrieres?