The Justice Department announced Thursday that it has ended a lengthy investigation into the CIA's interrogation and treatment of prisoners without bringing any criminal charges.

U.S. Attorney General Eric Holder announced the investigation into the deaths of two suspected terrorists who died in CIA custody -- one in Iraq and another in Afghanistan -- was ended without charges because "the admissible evidence would not be sufficient to obtain and sustain a conviction beyond a reasonable doubt."

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The two cases include the highly publicized case of Manadel al-Jamadi, who died in a shower stall at the infamous Abu Ghraib prison in Iraq while in CIA custody. Several U.S. soldiers, who were photographed with al-Jamadi's body, packed in ice inside a body bag, were later prosecuted and convicted in military courts for prisoner abuse.

The investigation spanned more than four years. It began with an investigation into the CIA's destruction of videotapes of aggressive interrogations of terrorist suspects, but was later expanded to include the deaths of the two detainees.

In all the Justice Department investigated the treatment of 101 detainees who been held in U.S. custody since 9/11.

CIA Director David Petraeus issued a statement thanking everyone at the CIA who supported the Justice Departments investigations.

In an apparent effort to put the incidents and investigations to rest, Petraeus added, "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."

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