A U.S. military prosecutor at Guantanamo Bay has quit because of what he described as ethical disputes with his superiors, alleging they suppressed evidence that could help clear a young Afghan detainee of war crimes.

The prosecutor, Army Lt. Col. Darrel Vandeveld, described the disagreements in a statement supporting a defense bid to dismiss the charges against Mohammed Jawad. A copy was obtained Wednesday by The Associated Press.

"Potentially exculpatory evidence has not been provided," Vandeveld wrote, citing a failure by "prosecutors and officers of the court."

The disclosure triggered new attacks on the integrity of the Pentagon's military tribunal system, which has faced accusations of ethical lapses and political interference from other insiders including a former chief prosecutor.

The current chief prosecutor, Army Col. Lawrence Morris, denied that his office withheld evidence and said there was no basis to Vandeveld's ethical qualms. He said Vandeveld told him he was leaving his post for "personal reasons."

"All you have is someone who is disappointed because his superiors didn't see the wisdom of his recommendations in a case," Morris told reporters.

Jawad, who was captured in Afghanistan when he was 16 or 17, is accused of throwing a grenade that wounded two American soldiers and their interpreter in December 2002. He faces a maximum life sentence at a trial scheduled to begin in December.

Vandeveld said prosecutors knew that Jawad may have been drugged before the attack and that the Afghan Interior Ministry said two other men had confessed to the same crime, according to Michael Berrigan, deputy chief defense counsel for the Guantanamo tribunals.

In his written declaration, Vandeveld said he wanted to offer Jawad a plea deal that would allow him to receive rehabilitation during a short period of additional confinement. His bosses disagreed.

"As a juvenile at the time of his capture, Jawad should have been segregated from the adult detainees, and some serious attempt made to rehabilitate him," Vandeveld wrote. "I am bothered by the fact that this was not done."

Vandeveld declined to comment through a tribunal spokeswoman.

Jawad's lead attorney, Air Force Maj. David Frakt, said he asked for Vandeveld to testify at Jawad's pretrial hearing Thursday but he was denied authorization to fly to the U.S. Navy base in southeast Cuba.

"He decided he could no longer ethically serve either as a prosecutor in this case or for the Office of Military Commissions," Frakt told reporters.

At least three other Guantanamo prosecutors have quit their posts with grievances about the process. The former chief prosecutor, Air Force Col. Morris Davis, resigned in October and accused his superiors of political meddling.

Davis testified last month that a Pentagon official who oversaw the tribunals until last week, Air Force Brig. Gen. Thomas Hartmann, pushed for Jawad to be prosecuted before others because the details of the case would grip the American public and help build support for the process.

"The guy who threw the grenade was always at the top of the list," Davis said.

The military judge later ruled that disqualified Hartmann from the case, saying he had compromised his objectivity by aligning himself with prosecutors.

Two other former prosecutors, Air Force Maj. John Carr and Air Force Maj. Robert Preston, asked to be reassigned after alleging in 2004 that prosecutors deliberately misled senior civilian Pentagon officials about the quality of evidence against defendants.

"This appears to be yet another example of the government pushing the commission's case forward with total disregard of the truth or the rules," said Jennifer Daskal, senior counterterrorism counsel for Human Rights Watch.

Jawad is one of roughly two dozen Guantanamo detainees facing charges. Military prosecutors say they plan trials for about 80 of the 255 men held here on suspicion of links to Al Qaeda or the Taliban.