pardon me for intruding, but it seems to me that he's stalling for time. As a 3rd party not involved, I suggest (in my own opinion of course) that if you're intending to take action, the sooner the better. The more time you give him, the more time he has to prepare a defence and get rid of any evidence that he can.
Printing screenshots are not a solid piece of evidence, as an any competent lawyer will argue that as digital photographers, you have the skills necessary to "create" the images with photoshop or similar programs. Cached versions of the offending site are more reliable, but once again not entirely bulletproof if faced with a competent lawyer. He doesn't seem to remorseful either, what with the fake I/C, and not admitting it until someone noticed it was fake. I wouldn't put much into his claim that he's an 18 year-old student either.
Of course, the other possibility is that he is not the perp you guys are looking for, and that he's just some troll looking for fun at the expense of others.
Whatever the case, I hope you guys get some justice, and this "joeriteexposure" learns the hard way that you can't just rip off the hard work of other photographers and expect to get away with a simple "sorry" online.