CLAYTON CRAMER: Mentally ill have been left to fend for themselves. The result? Random acts of mass murder.

Why am I pointing to deinstitutionalization? First, statistical evidence from professor Steven P. Segal at the University of California, Berkeley demonstrates that 27 percent of the state-to-state variation in murder rates is associated with ease of involuntary commitment. Similarly, University of Chicago professor Bernard Harcourt’s work on murder rates and mental-hospital lockup rates shows a statistical connection.

Second, even countries with generally stricter gun-control laws still have these random mass murders with guns, and they aren’t less common than in the U.S. You just don’t hear about them here.