Some people are just interested in that stuff. I'd be a little more scared if he was looking up how to make explosives. And even then, no one serious about carrying out some sort of attack would be doing their research in class where everyone can see.
I've been called out on saying 'creepy' or 'suspicious' things now and then and I usually want to respond that if I had negative intentions, I wouldn't have been public about it. Unfortunately people might not necessarily react to that too well either. #6 is right.