The Justice Department on Thursday closed its criminal investigation of the deaths of two prisoners in CIA custody, ending a controversial investigation that Attorney General Eric Holder had approved more than a year ago.

The investigation, conducted by veteran Justice prosecutor John Durham, examined alleged CIA interrogation abuses in connection with prisoner deaths at Abu Ghraib prison in Iraq in 2003 and at a secret prison in Afghanistan in 2002.

If the probe had led to criminal charges against CIA officers or contractors, it could have ignited a firestorm of objections by Republican lawmakers and the national security community.

Holder acknowledged that he made a controversial decision to appointed Durham in 2009 to examine allegations of CIA interrogation abuses in about 100 cases. His aides say he was aware the Obama White House wanted the torture controversies put behind it, but Holder pressed on. Republican lawmakers and the CIA were upset about the new review of alleged detainee mistreatment.

In June 2011, Durham concluded that nearly all of the allegations should not be prosecuted. However, he said he would look into two cases in which prisoners died while in custody. On Thursday, Holder said no charges would be brought in those cases.

"Assistant U.S. Attorney John Durham has now completed his investigations, and the Department has decided not to initiate criminal charges in these matters," Holder said in a written statement. While praising the work of the men and women in the U.S. intelligence community, he left unanswered whether he believes inappropriate actions were taken against prisoners during the wars in Iraq and Afghanistan.

"Our inquiry was limited to a determination of whether prosecutable offenses were committed and was not intended to, and does not resolve, broader questions regarding the propriety of the examined conduct," Holder said.

CIA Director David Petraeus sent a statement to all CIA employees marking the end of the investigation and ignoring the lingering controversies. "As intelligence officers, our inclination, of course, is to look ahead to the challenges of the future rather than backwards at those of the past. Nonetheless it was very important that we supported fully the Justice Department in its efforts," he said.