I was going to reference this study as well. Decided I didn't want to get in the middle of a discussion that has a tendency to bring out a passionate argument from both sides. Now that you brought it up....geeze, I'll dive in. Just yesterday evening, I listened to a Doctor reference studies related to use of cannabis and crimes of anger. He said, when minors commit crimes there is a push to study the "how and why' these crimes are committed. Studies show more often than not, minors who commit crime can be associated with smoking pot. He went on to say, crimes committed by adults aren't studied as much. But did say, the recent shooting show that both assailants were indeed avid pot smokers. When tendency toward mental illness is coupled with cannabis, it becomes a problem.
It is very likely that this is merely a correlation, not a cause. Most likely, those who have a tendency toward violence may turn to cannabis to self medicate. I don't advocate using cannabis, but it has a long history of medical use before pharmaceuticals became common, and most certainly would be preferred over opioids.