That's very true SPB-Cooperator. One could hardly monitor gun-owners throughout their lives. I believe here in UK the licence-holder can have his arrangements inspected by the Police at intervals (in other words, to make sure the locked cabinet is still kept secure, and the ammunition is locked away separately from the firearm) But guns can and do end up in the wrong hands.

However, it's also wise to examine this youngster's mindset, to better understand how all this happened. His father had died a while ago and his mother fairly recently, so he was an orphan. He was behaving oddly and was seriously disturbed judging by his social media postings. With all the publicity awarded to school shootings (naturally) it's a way for an isolate to make his/her point.

Please don't think I'm excusing this evil, I'm not. But there were several warnings about this man which were not addressed.

I wasn't going to post this, but - my uncle (many, many years ago) blew his brains out with a sports gun one morning as his children were getting ready for school. He and my aunt were crack shots in a gun club. The children (my two cousins) ran into the bedroom hearing the explosion and...well, one can imagine. My aunt was arrested for a while as she was a suspect until the children verified that she had been in the kitchen when he pulled the trigger.
No-one ever discovered why he did it, there were no signs of depression and no suicide note. It definitely wasn't an accident.
Guns are terrible things. Guns kill...