snitches get stitches
Snitching doesn't seem to be consistent with his character. It was reported that he decided to work with the FBI because he has a young child and he doesn't want to abandon him. He would have received a very severe prison sentence had he not cooperated.
The FBI claims that they were able to figure out who he was when Sabu went on IRC without masking his IP. I don't believe this. I think he was too careful and too paranoid to make this mistake, although it is possible. I think that he got careless when he cross contaminated his accounts. When a few other hackers exposed him, they had found email accounts and forum handles that he used in the past that were similar to the handles he used as Sabu. This was a huge mistake.
I think the FBI had a good idea who he was and then, either through a subpoena to his ISP or through a compromised TOR server, got enough evidence to identify him with enough certainty to justify getting a warrant to search his home.
While I don't agree with some of the things Anonymous (and the other groups he was part of) have done, I think they've done some good things. Hopefully, for their sake, they will change their ways and understand that they can't trust anyone.