Now that he has admitted to doing this can he be held liable?

Probably not.

My guess is that he's probably just a coked-out lunatic screaming for attention in a society that values fake Internet points more than establishing real world relationships with other human beings. Sane people don't normally rock back and forth while screaming at their computer.

A few of the hacks he's claiming credit for were also claimed by other "hackers".

I hope he gets investigated, but just because he says he did something, doesn't make it so.