The only real consensus I found [in the literature] was that these types of school shootings, or even spree killings, are too rare to do any kind of meaningful analysis of cause and effect… There’s more variables than there are data points. So you can’t do any kind of meaningful analysis. So we just don’t know what the important influences are and policies might reduce the risk of this happening again in the future.

Dr. Steven Novella, on the Skeptics Guide to the Universe #388

Everyone has been rushing to find a solution to these types of incidents. It must be guns, it must be violent video games, it must be because we don’t have armed security, it must be because of mental illness. The truth is we just don’t know.