And they're not grounds in and of themselves for any official action. Combine them with taking ammunition to a prohibited place (a school), making threats, etc., though, and there's probably enough to justify a warrant, which could lead to further evidence.
As I was typing this, Riley's post immediately above appeared. It looks like there was more than enough evidence to do some serious digging, probably to include warrants. Even making the threat without bringing live ammo to school is probably close enough to the "making terroristic threats" statutes to get something done.
Not being facetious or anything, serious question here. Say he had 45 fully loaded 30rd pmags and 2 M4 clones locked up in a gun safe. Lets say it was all purchased and possessed legally. Then what? Are you talking arrest warrants or search warrants? This is a slippery slope and it got there really quickly. Personally I'm just as leery of all the "see something, say something" talk as I am the gun control talk.
There's no quick fix to this, the real problem is instant worldwide access to live media promoting emotional, sensationalistic events nonstop 24/7/365. Couple that with evil bastards doing evil things and it has an effect on society. Society is going to have to learn to parse things and get back to what's important. Gun control, mental institutions, etc. isn't going to fix a damn thing. Society is broken...