I wouldn't be surprised to hear that someone who attacked strangers for no apparent reason was experiencing delusions or hallucinations. I would be surprised to hear that someone with sociopathy did so, because they normally hurt people only for personal gain, and there's nothing to gain from opening fire on a crowd.
People with schizophrenia usually do not attack people for no reason either. The independent association of schizophrenia with violent behavior is low, and most of the difference in rates of violence between schizophrenics and non schizophrenics seems to be attributable to the higher rate of substance abuse among schizophrenics.
If you know that someone is a mass murderer, it should give you a high posterior probability assessment for mental illness, but not a high probability assessment for schizophrenia.
Most sociopaths are not mass murderers or serial killers, but as best I can determine (I've found articles that allude to it, but none that give an actual percentage, and wikipedia pages for individual mass murderers seem to support it) most mass murderers and serial killers are sociopaths. However, most mass murderers and serial killers are not schizophrenics, although it seems that a significantly greater proportion of serial killers and mass murderers are schizophrenics than the proportion of the population in non mass murderers or serial killers.
Sorry, you're right. I spent last year working on a psych ward, and I agree that most people with schizophrenia are unlikely to hurt others.
My guess is that mass murderers with some ideological or practical reason for choosing the people they murder are more likely to be sociopaths. I can't think of a reason to target people at a movie theater, which makes me put a higher prior on delusions or hallucinations in this case.
A Ph.D student in neuroscience shot at least 50 people at a showing of the new Batman movie. He also appears to have released some kind of gas from a canister. Because of his educational background this person almost certainly knows a lot about molecular biology. How long will it be (if ever) before a typical bio-science Ph.D will have the capacity to kill, say,a million people?
Edit: I'm not claiming that this event should cause a fully informed person to update on anything. Rather I was hoping that readers of this blog with strong life-science backgrounds could provide information that would help me and other interested readers assess the probability of future risks. Since this blog often deals with catastrophic risks and the social harms of irrationality and given that the events I described will likely dominate the U.S. news media for a few days I thought my question worth asking. Given the post's Karma rating (currently -4), however, I will update my beliefs about what constitutes an appropriate discussion post.