JOINT BASE LEWIS-MCCHORD, Wash. » Raging on steroids, fear and insecurity, Staff Sgt. Robert Bales threw himself into one of life’s great stress relievers: chopping wood. He sawed and hacked from morning till almost dusk, attacking a large tree he and his soldiers had laid low near their remote outpost in Kandahar province, Afghanistan.

It wasn’t enough.

Hours later, after drinking with his buddies, the soldier outfitted himself with a 9 mm pistol and an M-4 rifle, and headed out in the middle of the night to commit one of the worst atrocities of the Iraq and Afghanistan wars — the slaughter of 16 men, women and children in two nearby villages. Some screamed for mercy. Others didn’t even have a chance to get out of bed.

For the first time, Bales apologized for the attack Thursday as he addressed six jurors determining whether his life sentence will include the possibility of parole. Responding to gentle questioning from one of his defense attorneys, Emma Scanlan, the 40-year-old said he’d bring back the victims “in a heartbeat” if he could.

“I’m truly, truly sorry to those people whose families got taken away,” he said in a mostly steady voice. “I can’t comprehend their loss. I think about it every time I look at my kids.”

Bales, 40, pleaded guilty in June in a deal to avoid the death penalty. He did not recount specifics of the horrors in court Thursday or offer an explanation for the violence, but he described the killings as an “act of cowardice, behind a mask of fear, bulls—- and bravado.”

He said he hoped his words would be translated for the nine villagers who traveled from Afghanistan to testify against him — none of whom elected to be in court to hear from him.

The father of two from Lake Tapps, Wash., was serving his fourth combat deployment when he left his outpost at Camp Belambay, in Kandahar province, in the middle of the night to attack two villages, exhibiting an unimaginable brutality as he gunned down his victims and set some of their bodies, stacked like wood, on fire with a kerosene lantern.

His attorneys have made much of Bales’ 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 psychiatrists or other doctors, saying they saw little point in making the case a battle of the experts.

Instead, they had Bales and some of his fellow soldiers to testify about the difficulties they endured and the images that stuck with them after earlier tours in Iraq. They rested their defense after Bales finished speaking, and closing arguments were scheduled Friday morning.

If the defense can convince two of six jurors that Bales deserves leniency because he was a good soldier who simply snapped, he would be eligible for parole in 20 years.

Bales said he was nervous to address the court, and he sat at the witness stand as his wife cried in the front row of the courtroom. He sometimes 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.”

His statements were not made under oath, which prevented prosecutors from cross-examining him. But in their questions of other witnesses, they noted Bales’ checkered past, including a fraud investigation and eventual $1.5 million judgment, a drunken-driving arrest in 2005, a driving under the influence crash in 2008, and lies on re-enlistment documents about his criminal history.

The hearing began Tuesday, with nine Afghans — some angry and at least one cursing Bales — testifying over two days about their lives since the attacks.

“If someone loses one child, you can imagine how devastated their life would be,” said Haji Mohammad Wazir, who lost 11 family members, including his mother, wife and six of his seven children. “If anybody speaks to me about the incident … I feel the same, like it’s happening right now.”

Bales’ lawyers did their best to paint a sympathetic picture.

Former pro football player Marc Edwards testified Thursday as a character witness, telling jurors he remembered Bales as a great leader from their high school days in Norwood, Ohio.

Wearing the Super Bowl ring he won with the New England Patriots in 2002, Edwards said the slightly older Bales was magnanimous when Edwards took his position at starting linebacker.

Jurors on Thursday also heard from two soldiers who served with Bales in Iraq. One described how they sometimes had to collect the bodies of casualties, and how Bales helped carry wounded civilians — many severely burned — at the Battle of Zarqa in 2007.

Another soldier, Maj. Brent Clemmer, said it was unfathomable to learn that the competent, positive soldier he knew could have committed the killings.

“I walked myself into my office, poured myself a glass of scotch, and cried,” he said.

The final act for the defense came with Bales taking the stand.

He described 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.

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 in ways he’s embarrassed about.

Bales said he spent almost the entire day before the murders venting his anger on the downed tree. The tree had served as a “marker” for enemy fighters calling in attacks or setting roadside bombs, and the process of felling it with explosives left Bales and his comrades vulnerable.

He never did finish cutting it up.

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