The U.S. soldier who massacred 16 Afghan civilians apologized Thursday for his "act of cowardice" as he made his case at his sentencing hearing for why he should someday have a chance at freedom.

Staff Sgt. Robert Bales he said he was angry and afraid when he went on a solo nighttime mission and slaughtered villagers, mostly women and children, on March 11, 2012 in their huts. The massacre prompted such angry protests that the U.S. temporarily halted combat operations, and it was three weeks before Army investigators could reach the crime scene.

Bales did not recount specifics but described the attack as "an act of cowardice, behind a mask of fear, bullshit and bravado."

"I'm truly, truly sorry to those people whose families got taken away," he said. "If I could bring their family members back, I would in a heartbeat."

Bales, 40, pleaded guilty in June in a deal to avoid the death penalty for the attacks. A military jury will determine if his life sentence should offer a chance of parole.

If he is sentenced to life with the possibility of parole, Bales would be eligible in 20 years, but there's no guarantee he would receive it. He will receive life with parole unless at least five of the six jurors say otherwise.

Bales, a father of two, said he was mad at himself for being angry all the time, drinking too much and hiding his problems.

He was nervous when he took the stand as the final witness in the hearing at which his lawyers have tried paint a sympathetic picture of the soldier to contrast his own admissions and the testimony of angry Afghan villagers about the horror he wrought.

Apologizes to comrades

As Bales testified, his wife cried in the front row of the courtroom. Bales himself briefly became emotional, especially choking up as he apologized to his fellow soldiers.

"I love the Army, I've stood next to some really good guys, some real heroes," he said. "I can't say I'm sorry to those guys enough.

"Nothing makes it right," he added. "So many times before I've asked myself. I don't know why. Sorry just isn't good enough. I'm sorry."

Bales said he hoped his words Thursday would be translated for the villagers, none of whom was in the courtroom.

"I can't comprehend their loss. I think about it every time I look at my kids," Bales said.

The defence followed two days of testimony from nine Afghans, who spoke of their lives since the attacks.

Haji Mohammad Wazir, lost 11 family members, including his mother, wife and six of his seven children, told the six-member jury Wednesday that the attacks destroyed what had been a happy life. He was in another village with his youngest son, now 5-year-old Habib Shah, during the attack.

Bales was serving his fourth combat deployment when he left the outpost at Camp Belambay in the pre-dawn darkness. He first attacked one village, returning to Belambay only when he realized he was low on ammunition, said prosecutor Lt. Col. Jay Morse.

Bales then left to attack another village.

Bales' attorneys previously made much of his repeated deployments and suggested that post-traumatic stress disorder and traumatic brain injury may have played a role in the killings. But they offered no testimony from medical experts on that point, saying they saw little point in making the case a battle of the experts.

Closing arguments on Friday

Instead, they rested their defence after Bales finished speaking Thursday. Closing arguments were scheduled Friday morning.

Bales described in detail the trouble he had readjusting to civilian life after his deployments to Iraq. He became angry all the time, he said, and he was mad at himself for that.

"Normal course of life became hard in that, you know, waiting in traffic, terrible," he said. "Certain smells would just drive me nuts. Washing the dishes I'd just be mad about, for no reason."

He began drinking heavily, hiding bottles and sleeping pills from his wife. He fleetingly began to see a counselor, but quit because he didn't think it was working and he didn't want others to find him weak.

His perpetual rage worsened as he deployed to Afghanistan in late 2011, taking steroids while there. He lashed out frequently at junior soldiers, he said, in ways he's now embarrassed about.

Bales said he spent almost the entire day before the murders venting his anger by chopping and sawing a large tree that the soldiers had taken down near the base.