[T]he best predictor of violent behavior is a previous history of violent behavior, which we now know that the Miami man had. He was apparently the first person ever to be tasered by North Miami Beach police. Why? He had beaten and was threatening to kill his mother.
How drugs relate to violence:
When taken by mentally ill people … drugs can dramatically increase the risk of violence. A 2009 review of the research found that while having schizophrenia itself may raise a man’s risk of violent behavior by two to four times, drug misuse may multiply that risk by a factor of 12. By itself, schizophrenia — with or without substance misuse — increases a person’s chance of committing homicide by a factor of nearly 20. And yet, in the press, drugs continue to get the primary blame for such crimes.
Jack Shafer has a primer on the face-eater's drug of choice, bath salts:
Tragically, the media-inspired drug-scare cycle tends to raise the awareness of a "new" drug at the expense of the drugs that have a greater impact on public health (alcohol, tobacco). Even worse, scare stories end up promoting the new drug better than any Madison Avenue campaign ever could, creating a "boomerang effect."