What no one seems to look at is the REAL cause for the massacre was sin, and sin is born out of lust, and this guy’s lust was to fulfill his fantasy that he was a larger than life character that wielded the power of life and death over innocent people. Is he wacked out of his head? Yes. Did he know it was wrong to shoot those people? Definitely. But in his lust to play the Joker, he put his desires above all others, even their very lives. What caused him to do it? Acting on his sinful desires.
Thank you for cutting to the chase and describing what happened from a biblical, theologically correct position = the root of the problem - sin, the motivation behind his henious actions - his own lusts, and the fact that he alone bears responsibility for his crimes, not “guns” or movies, etc.