[Pyrrho]

At this point I have seen no speculation as to what mind or mood altering substances this murderer may have been using. Easy enough to speculate about the effects of culture on the human psyche, except that I consistently notice a tendency toward blindness regarding drug and alcohol abuse. It rarely enters the discussion, and even then, the focus tends to be on whether or not the murderer had been under psychiatric care and what prescription drugs they had been taking.

That said, humans don't necessarily need outside influences to be homicidal. It's in the nature of the beast.