Comey's leak investigation

There's something from Comey's testimony (pdf) that jumped out at me:

SCHUMER: Have you ever had the opportunity to recall these (hospital) events on the record in any other forum?
COMEY: No.
SCHUMER: OK. And...
COMEY: I should...
SCHUMER: Go ahead.
COMEY: I was interviewed by the FBI and discussed these events in connection with a leak investigation the FBI was conducting.

I'm not exactly sure what it means, but it's pretty interesting - we learn that:
a) Comey was interviewed by the FBI regarding a leak investigation
b) The near-hospital-massacre was, apparently, relevant to the investigation.
c) Comey (either advertently or inadvertently, but certainly, unnecessarily) specified in his testimony that it was a leak investigation.

Which 'leak investigation' Comey is referring to? I'm tempted to hope/wish that Comey was referring to the AIPAC case, but he was probably referring to the investigation into who leaked to Risen and Lichtblau for their December 16, 2005 front-pager in the NYT.

As emptywheel wrote in March 06:

"At some point, I suspect James Comey will out himself as one of Risen's sources, and in so doing make it quite clear how Bush broke the law. If Comey does so, the Administration's attacks on Risen will appear nothing but churlish"

If this is indeed the leak investigation that Comey was referring to in his testimony this week, it's interesting that he mentioned the hospital 'anecdote' to the FBI investigators - presumably in his defense for leaking?