Yeah its a very hard thing to figure out and to help someone. And it has happened to me with friends (not with a shooting range).
Its is said today (I dont have a news paper proving this) but the guy that did this was a NJ state correction officer. He had his own gun but they are saying he went there and rented one. He left behind a wife and a 8 year old child.
I guess we cant know what is going on in other peoples heads and lives to make them do something like that.