Col Vendeveld wanted to negotiate a plea deal, defence lawyers say
A US military prosecutor at Guantanamo Bay has resigned in what defence lawyers describe as a row over ethics.
Lt Col Darrel Vandeveld had quit because his office suppressed evidence that could have cleared a client, defence lawyer Major David Frakt said.
The chief prosecutor has confirmed the resignation, but he denied withholding any evidence.
The case involves an Afghan detainee accused of throwing a grenade at a US military jeep, injuring three people.
The prosecution is said to have withheld evidence that others had confessed to carrying out the attack.
Col Vandeveld is the fourth Guantanamo military prosecutor to quit.
Col Lawrence Morris, the Guantanamo military commissions chief prosecutor, told reporters that there were no grounds for Col Vandeveld's "ethical qualms".
"All you have is somebody who is disappointed that his superiors didn't see the wisdom of his recommendations in the case," Col Morris said.
Maj Frakt told reporters that Col Vandeveld had wanted to negotiate a plea deal for the detainee, but that his superiors had blocked this.
Col Vandeveld has not commented publically, but made his concerns known in an declaration to the military court at Guantanamo Bay.
The declaration can only be made public by a tribunal judge, but in a copy obtained by the Associated Press news agency, Col Vandeveld wrote that "potentially exculpatory evidence has not been provided".
He blamed this on a failure by "prosecutors and officers of the court".
Col Vandeveld was prosecuting Mohammed Jawad, 24, who is accused of tossing a grenade into a military jeep at a bazaar in Kabul in 2002, injuring two US soldiers and their Afghan interpreter.
Col Vandeveld said prosecutors knew that Mr Jawad might have been drugged before the attack, and that the Afghan interior ministry said two other men had confessed to the same crime.
He also expressed concerns over Mr Jawad's treatment.
"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," Col Vandeveld wrote in his declaration.
"I am bothered by the fact that this was not done."
In August, a military judge ruling barred the tribunal's legal adviser, Air Force Brig Gen Thomas Hartmann, from Mr Jawad's case, accusing him of having compromised his objectivity.
Brig Gen Hartmann allegedly "pushed" for Mr Jawad to be charged because of the "gripping" details of his case.
The judge, Col Steve Henley, said that Brig Gen Hartmann's public statements aligning himself with prosecutors and defending the Pentagon's system for prosecuting terror suspects had compromised his objectivity.