Holder said he recused himself early on in the DOJ's investigation of what he described as serious leaks from government officials that jeopardized national security.
He said because he recused himself early in the investigation, he did not have all the facts surrounding the investigation.
"I don't know all that went into the formulation of the subpoena," Holder said at a press conference on Tuesday.
Holder, however, did say the leak that sparked the subpoena was "a very serious leak."
Read more on The Hill's Blog Briefing Room.