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 . Opinion : Eric Holder should discuss leaks publicly . 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 . 5 things about the controversy surrounding AG Eric Holder . 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 could n't provide specific information on why the Justice Department did n't go directly to the AP .
Justice Department . response to probe says it followed rules in scrutiny of Associated Press . Congress wants to know when attorney general recused himself from leak probe . DOJ sought to find out who told AP about al Qaeda airliner crash . NEW : AP conducted more than 100 interviews , examined documents .