You have missed the point. A gun-free zone is an invitation to trouble. Those who wish to murder are going to take the easy road and do not choose to go after the local police station.
The root cause is societies broken moral compass. I seriously doubt the person was a regular church attendee. People used to kill themselves not everyone they could take along with them. The debate over guns is a side-show. Guns do not kill. The moral inadequacies of those who have access to guns is the issue.