Where did Adam learn to use guns? At home, like most mass shooters.

[Johonny]

24. Rita Hayworth "I don't know how to shoot. "

Orson Welles "It's easy, you just pull the trigger."

You don't exactly need vast knowledge to shoot a person, particularly a kid at close range. If it was hard to use guns there would be significantly less shooting deaths.

As to should people have known... hindsight is 20/20. Things don't always work out like this SNL skit;

Reporter: Did you know him?

Neighbor: Yes, he was a very nice boy, quiet, never caused any trouble. Always willing to help out.

Reporter: Are you surprised he shot Buckwheat today?

Neighbor: Oh, yes, very surprised.

Reporter: Why is that?

Neighbor: Well, it's Boxing Day today. You don't expect something like this to happen on a holiday.

Reporter: I see. Well, are you surprised that your neighbor shot Buckwheat?

Neighbor: Oh, no, not at all. We all knew he'd try to kill Buckwheat someday. That's all he used to talk about. Even when he was little, he used to say 'Someday when I grow up I'm gonna kill Buckwheat'. He used to make all the other little kids play a game he made up called 'Kill Buckwheat'. He even wrote a song called 'Die, Buckwheat, Die' that he would play at parties. He would draw and paint pictures and give them to us as gifts. He was very generous that way. I have a piece he titled 'Dead Buckwheat #1627' hanging in my living room behind the couch.