@JohnAustin
Almost by definition, someone who commits a mass shooting has to have reached the point of psychosis. The 4chan/8chan shooters seem like they were sort of willfully trolled into it by transgressive eggers-on, but it's hard to say for sure. Every case is so unique. It's never just-this or just-that, it's a volatile mixture of things. True psychosis usually involves hallucinations, delusions etc. which may even, per experts like Thomas Szaz, be "normal" within dysfunctional families.