An attorney for an Oklahoma soldier convicted of killing an unarmed Iraqi prison detainee asked a military appeals court on Monday to overturn the conviction, in part because the prosecution had not revealed that a crime scene expert hired by the military supported the soldier's claim of self-defense.

The U.S. Court of Appeals for the Armed Forces heard arguments in Washington, D.C., in the appeal by 1st Lt. Michael Behenna of Edmond. Behenna was convicted in 2009 of unpremeditated murder in a combat zone and sentenced to 15 years in prison.

"The judges were very attentive. They obviously knew the record at trial," said Behenna's attorney, Jack Zimmerman.

"We know better than to try to predict an outcome, but we were very pleased with the depth of knowledge of the judges," Zimmerman said. "They clearly understood our position."

Prosecutors say Behenna took detainee Ali Monsour Mohammed to a secluded railroad culvert and shot him execution-style after interrogating the man at gunpoint about an April 2008 roadside bombing that killed two men under Behenna's command.

Zimmerman argued the conviction should be overturned because Army prosecutors failed to notify the defense that a crime scene expert retained by the military agreed with Behenna's claim that he shot the man in self-defense when the man reached for Behenna's handgun. Zimmerman also contends the judge at Behenna's military trial gave faulty jury instructions that took away his claim of self-defense.

The Army argued Behenna could not claim self-defense because he was pointing his weapon at the man when the man allegedly reached for Behenna's handgun.

There was no indication when the appeals court might rule.

Behenna, 28, is serving his sentence at Fort Leavenworth, Kan. His mother, Vicki Behenna of Edmond, attended Monday's hearing and said it was difficult to judge how the court might be leaning.

"I got mixed feelings, this court was very well prepared, they knew the facts and knew the law," said Vicki Behenna, an assistant U.S. attorney for the western district of Oklahoma.

She said her son had called various family members "six or seven times" Monday to gauge their reaction to the arguments. She said his girlfriend also visited him last week.

"She said he seemed really composed, looking at this as an opportunity, but a little apprehensive at what might happen," Vicki Behenna said.