(REUTERS) - An army lieutenant found guilty of murdering two Afghan civilians was being used as a "scapegoat"by the United States (US) Army, his lawyer said on Friday, predicting that the officer's conviction and a 20-year sentence would be overturned on appeal.

Prosecutors at Fort Bragg, North Carolina, accused 1st Lieutenant Clint Lorance, 28, of illegally ordering the fatal shootings of two men on motorcycles while on patrol in Afghanistan's Kandahar province in July last year. He was found guilty on Thursday of two counts of murder.

Lorance's attorney, Ret. Lieutenant Colonel Guy Womack, said his client had given a legitimate order to soldiers in his platoon to open fire on the approaching motorcycles, suspecting they were Taleban suicide bombers armed with an improvised explosive device, or IED.

"One of his men asked for permission to fire and he gave the order 'engage.' It was a legitimate operation," said Mr Womack.

"They were attacked outside the wire the day before, and there were intercepted communications that enemy in the area were watching, with radios, pointing out US positions and movements of our men," he said.

Lorance, who joined the Army in 2003, had very little experience in Afghanistan and was on his second combat patrol after having taken command of his platoon only a few days earlier, Mr Womack said.

"The Army is using him as a scapegoat so they can tell the Afghan government the person who killed the civilians is being punished," said Mr Womack.

Lorance was accused of violating the rules of engagement and ordering his men to open fire without first establishing if there was a proper hostile threat.

After the shooting, Lorance tried to hide evidence that the two dead Afghans were carrying proper identity, something the Taleban rarely do. "He told his soldiers to forget they saw the IDs. That was wrong," said Mr Womack.

Prosecutors told the jury that Lorance had been overly aggressive and had threatened to shoot an Afghan farmer the day before during an argument over access to the farmer's land.

Lorance, who grew up in Oklahoma, was also found guilty of the attempted murder of a third Afghan, making an illegal threat, and obstructing the investigation.

Mr Womack said Lorance could be granted clemency by his commanding officer after the trial transcript had been reviewed, and under the military justice system an automatic appeal would be heard.

Several members of his family attended the court martial and vowed to fight for his freedom.

His mother Anna Lorance, who lives in Celeste, Texas, has launched an internet petition saying her son was "protecting his men" from the Taleban.