Washington (CNN) -- The Justice Department defended its scrutiny of reporters around a high-profile national security leak investigation, saying on Tuesday that it followed its own regulations in acquiring subpoenas for Associated Press phone records.
But a letter from Peter Kadzik, principal deputy assistant attorney general, to members of Congress failed to answer a key question asked by lawmakers: When did Attorney General Eric Holder formally recuse himself from the leak investigation?
Holder said in congressional testimony that he took that step to avoid a possible conflict of interest because he had been interviewed about the leak during the course of the investigation.
That investigation centered on who told the AP about a 2012 plot by an al Qaeda affiliate in Yemen to bomb an airliner.
The issue has generated sharp political controversy. Lawmakers have claimed investigative overreach by the Obama administration and media outlets have expressed concerned about the potential chilling effect of such efforts on press freedoms.
Specifically, the Republicans are concerned about whether Holder was being truthful during May 15 congressional testimony.
"With regard to potential prosecution of the press for the disclosure of material, that is not something that I have ever been involved in, heard of, or would think would be a wise policy," Holder said.
It later came to light Holder had authorized a search warrants for e-mails and subpoenas for phone records in another leak case in which the government indicated a TV reporter was suspected of breaking the law. This stoked more controversy.
The letter from Kadzik in response to congressional follow-up to Holder's testimony said Deputy Attorney General James Cole, who approved the subpoenas for the AP records, also had been interviewed by investigators during the leak probe.
According to the letter, Cole did not have any contacts with the media at the time "thus avoiding the appearance of a conflict of interest."
The subpoenas involved records for more than 20 AP phone lines for part of April and May 2012.
The toll records would show what numbers were dialed from the AP lines and what numbers dialed in, but would not provide any information on the content of conversations.
According to the letter to the House Judiciary Committee, the Justice Department followed its rules and exhausted other methods to find out who might have leaked the classified information before seeking the phone records.
The letter said investigators conducted more than 550 interviews and examined tens of thousands of pages of documents before issuing subpoenas involving the AP lines.
Justice Department rules call for negotiations with news organizations on such issues unless there is a "substantial threat to the integrity of the investigation."
The Justice Department said because the investigation was ongoing it couldn't provide specific information on why the Justice Department didn't go directly to the AP.