I guess because I do most of my social interaction online I'm much more open and honest than I am IRL. I come across fairly reserved, quiet and unfriendly IRL but online I'm, err.. different. And more myself. I've never felt from all the tens of people that I've met IRL that they were a significantly different person than on the internet - I think even if they take certain steps to hide or alter a part of their personality, it always shines through, you can tell that something isn't right. I'm not sure the person you meet IRL is any more authentic than the person you talk to online. I make some very small effort not to paste my dox everywhere but then I've been online a lot for err, nine years? I'm pretty sure everything is out there by now. If someone wanted my address or anything they'd be quite welcome to it if they had a valid reason.
To me, that works for Terry, too (from what I know, I didnt know him personally) - maybe he really was a fairly normal pokemon playing kid who fucked up pretty hard due to circumstances outside his control. I don't think a person's life has too much influence on their behaviour, really - and I don't think that you can tell what anyone is going to do from knowing them in any way (i.e. I think if youd met up youd have not known anything different, either).
People can hide/mask/whatever parts of their personality and life, but I don't think it's got anything to do with online or IRL. It's easier to be the person you want to be online, but then without actually knowing someone's life very well you arent going to know what they're actually like, whether you see them every day at college or talk twice a week online.