[DanBC]

You didn't bother reading the post, did you?

Tucson: "Loughner had been arrested (but not convicted) once on a minor drug charge[11]" - drug addiction combined with mental illness is the predictor here. The mental illness alone was not predictive.

https://en.wikipedia.org/wiki/Jared_Lee_Loughner

> Acquaintances said that Loughner's personality had changed markedly in the years prior to the shooting, a period when he was also abusing alcohol and drugs.

Again: drug or alcohol addiction are reasonable predictors of violent behaviour. Mental illness alone is not a reasonable predictor of violence.

Mental illness is common. It would be unusual for there to be no mass murders with a mental illness. All you're doing is lazily ignoring all the very many murders committed by people who do not have a mental illnes o focus on a tiny minority committed by people who do have a mental illness; and then you're ignoring the actual predictors of violent behaviour which are previous violence or drug / alcohol addiction.