[devilshaircut]

Actually the article (in the quote the replier posted) uses statistics to so show, evidently, that drug users commit violence less frequently than a control group; the quote does not discount the causal effect of drugs and violence, much less in such a specific case.

The way to invalidate the poster's original claim is to show evidence that the violent behavior in that specific instance (or at least a comparable instance) was in no way related to the perpetrator's drug-influenced physiological state. I believe that would be difficult to demonstrate.