What Could’ve Motivated a Christian-Hating Atheist & Self-Proclaimed Social Justice Warrior to Attack Familiar Church?

Devin Kelley, the murderer of 27 Christians in a small-town church, had identified himself on Facebook as an atheist (really an agnostic) thinking Christians are stupid, priding himself on being a social justice warrior, so as the authorities ostensibly struggle to discover his motive for that murderous rampage, shouldn’t they consider that warriors go to battle, sometimes in literal ways when they are agitated, to attack a soft target, particularly one familiar?