The investigation is pretty limited on this. Very few people were briefed on this.
I am not so sure that it was anyone at the NSA, I think it was a Senator or a Congressman- those that were briefed. Or it could be someone in the FISA courts.
The CIA leaks like a sive- we know this. Just reading the Washington Post story, you could clearly get the feeling that someone from the inside of the CIA was leaking this story. But reading the NY Times story- you cannot get the same feeling that the NSA was leaking this. The NY Times gave the impression that it was a "lawmaker"- leading us to believe that it was someone involved in the Congress.
Didn't Judge Robertson just resign?
The original Slimes story cited NSA employees, IIRC.