Part of the issue here is that just because he submitted a write up on what he claims he did doesn't mean he didn't leave a backdoor. Chances are he didn't but until they analyze everything (which takes forever given the number of servers a university department has), how do they know? It could be a way of covering tracks.
Look at it this way, you got home one day and found a 16 page write-up about how a guy broke into your house, disabled the motion detector, and finally video taped it all, how would you feel? Jail is beyond what I would do personally but I'm pretty sure I wouldn't be peachy for such a kind gesture.