Feb. 9, 2012  -- The Department of Defense is reviewing the Air Force's investigation into a deadly F-22 jet crash that claimed the life of fighter pilot Capt. Jeff Haney -- a crash that the Air Force blamed on Haney, despite a malfunction that caused his oxygen system to shut off mid-flight.

Launched by the Pentagon's Inspector General, the assessment aims to make sure the Air Force adhered to proper procedures during their investigation of the 2010 crash in the Alaskan wilderness and "will also verify that [the Air Force's] conclusions are supported by evidence of record consistent with standards of proof," according to a Jan. 25 letter from the Inspector General's office to the Secretary of the Air Force, as posted on the Air Force Magazine website.

In December the Air Force released its findings from an intense, months-long investigation into the crash, concluding that even though an unknown malfunction caused Haney's oxygen system to shut down -- leaving Haney to experience "a sense similar to suffocation" -- it was Haney's fault that the plane went down.

"By clear and convincing evidence, I find the cause of the mishap was the [pilot's] failure to recognize and initiate a timely dive recovery due to channelized attention, breakdown of visual scan and unrecognized spatial disorientation," the president of the investigation board, Brig. Gen. James Browne, said in conclusion. The report said Haney failed to activate his emergency oxygen system -- which the Air Force admitted is difficult to reach in winter gear -- or to take the plane low enough for him to simply take off his mask to breathe.

The stealth F-22 Raptor, America's most expensive jet at $143 million-a-pop, has been plagued with rare but potentially deadly apparent oxygen problems as pilots have reported "hypoxia-like symptoms" in several instances since 2008.

Family and friends of Haney's blasted the Air Force for its report on a Facebook memorial page for Haney, with one of the page's administrators writing, "So by this logic, next the Army will say soldiers killed in action were in fact not killed by enemy gun fire [but] they died from a lack of blood volume and intact organs [and] were at fault for not seeking medical attention in a timely manner."

READ: Air Force Blames Oxygen-Deprived Pilot in Deadly F-22 Crash

A spokesperson for the Pentagon's Inspector General's office told ABC News the additional review was self-initiated -- meaning it was not ordered by a member of Congress -- and does not yet have an expected completion date. The spokesperson said she could not comment on what compelled the office to conduct the review.

Air Force Guessing on Cause of Malfunction

Haney had just completed a routine training mission over Alaska in November 2010 and was returning to base when he suddenly went off radio contact, turned his plane into a downward dive before apparently trying to pull up at the last second -- just moments too late to save his life.

In addition to the released 40-odd-page public investigation report, ABC News has obtained nearly 1,000 pages of Air Force documents relating to the crash investigation through a Freedom of Information Act request.

Those documents show that the Air Force has been left guessing as to what caused an apparent leak in an engine system that automatically forced the plane to shut off Haney's oxygen. Their best guess, the documents revealed, is that there was a "leaking duct, valve, clamp or seal" somewhere.

Just moments before the malfunction, Haney appeared to be having fun after a successful training mission. His last words, according to a transcript of radio calls obtained by ABC News, was a taunting challenge to a fellow pilot: "Race you to CRUZR," he said, presumably referring to a checkpoint before heading back to base.

"He was kind of saying it joking, kind of just enjoying the night of flying, if you will," the other pilot, identified only as mishap flight leader, told Air Force investigators.

But then Haney disappeared from sight and was never seen again.

Pilot Had Received 'A' on Emergency Systems, USAF Omits Fellow Pilot's Crash Theory

In several interviews the Air Force conducted of fellow pilots as well as his superiors, Haney was described as an exceptional pilot -- "above average" when it came to most fighter pilot duties and one of the service's best. Two years before the crash, he had scored an "A" when tested on emergency systems and survival.

"He was kind of one of the more quiet guys in the squadron... [but] when he would speak, he would choose his words carefully and he normally said something worth listening to," Haney's squadron commander told investigators. "I think he was very happy. He struck me as a guy that was a natural fighter pilot that liked doing what he was doing and was very content."

The F-22 Raptor has had a history of apparent oxygen problems. Since 2008 pilots have reported more than a dozen instances of experiencing hypoxia-like symptoms mid-flight, according to the Air Force. The Air Force grounded the entire fleet of planes for nearly five months in 2011 while it investigated the possible cause of the problem but were never able to identify it and cautiously have allowed the planes back in the air. Those pilots, however, did not suffer a complete oxygen shut-off like Haney did and were able to guide the planes back to base without incident.

READ: F-22 Raptor Pilots Suffer More Apparent Oxygen Problems

The Air Force maintains that Haney was never incapacitated during the flight, despite a period of several seconds when he did not touch the plane's controls in the midst of his deadly freefall. Investigators said that Haney simply was too distracted by being not able to breathe to fly the plane.

But one of Haney's fellow pilots has another theory -- one that may never be public because it was omitted from official account. The pilot had chosen to share it with Air Force investigators off the record, the documents obtained by ABC News said.

Despite going combat operational in 2005, the F-22 Raptor has not seen combat and was not considered "an operational necessity" in any theater of combat from Libya to Iraq and Afghanistan, the Air Force said.

READ: The $77 Billion Fighter Jets That Have Never Gone to War

The Inspector General's letter was first reported by InsideDefense.com.

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