TACOMA, Washington (Reuters) - A U.S. Army sergeant who killed 16 Afghan civilians in cold blood last year pleaded guilty on Wednesday to premeditated murder and other charges under a deal with military prosecutors that spares him from the death penalty.

Staff Sergeant Robert Bales, a decorated veteran of four combat tours in Iraq and Afghanistan, admitted to leaving his Army post in the Afghan province of Kandahar last March to gun down and set fire to unarmed villagers, mostly women and children, in attacks on their family compounds.

“As far as why, I’ve asked that question a million times since then,” Bales said, in a calm, steady voice, when the judge pressed him for an explanation. “There is not a good reason in this world for why I did the horrible things that I did.”

The slayings marked the worst case of civilian slaughter blamed on a single, rogue U.S. soldier since the Vietnam War and further strained U.S.-Afghan relations after more than a decade of conflict in that country.

Bales, 39, now faces a life term in prison, but a military jury will decide if and when he will ever be eligible for parole after further proceedings set to begin August 19.

Prosecutors agreed not to seek the death penalty in return for Bales’ guilty plea to the murder charges he faced.

The judge, Army Colonel Jeffery Nance, accepted the agreement at the end of a lengthy hearing during which Bales was required to recount the events in question and to convince the judge he understood his plea and the consequences of his acts.

Wearing a military dress uniform, Bales stood beside his lawyer, Emma Scanlan, as she entered guilty pleas on his behalf to 16 counts of premeditated murder, six counts of attempted murder and seven counts of assault, as well as to alcohol and drug charges.

Reading through the list of charges himself, one at a time, later in the hearing, Bales acknowledged that he committed 10 of the slayings by shooting and burning his victims and that he killed six others by gunshot only.

“I then did kill her by shooting her with a firearm and burning her. This act was without legal justification,” he said during a matter-of-fact recitation of his crimes, delivered with no visible sign of emotion.

Army Staff Sergeant Robert Bales (L) and Judge Col. Jeffery R. Nance are seen in a sketch from January 17, 2013, as Bales is arraigned on 16 counts of premeditated murder, six counts of attempted murder and seven of assault at Joint Base Lewis-McChord, Washington. REUTERS/Peter Millett/Files

INTENT TO KILL

Asked by Nance if he had acted out of self-defense, or under orders, or whether he had any other legal justification to kill the 16 villagers, Bales replied, “No, sir.”

“Could you have avoided killing them if you wanted to?” the judge asked.

“Yes, sir,” he answered, adding that he “formed the intent (to kill) as I raised my weapon.” Bales said that setting fire to his victims was also done with the intent to kill, and that he was aware it was “against their cultural norms.”

Bales has claimed his memories of the killings are spotty, but he acknowledged seeing a lantern at one point during the rampage and that matches were later found in his possession. He said he learned from previous testimony that kerosene was used in the burnings.

Bales’ wife was seated behind him in the courtroom benches at Joint Base Lewis-McChord, near Tacoma, Washington.

Army prosecutors have said Bales acted alone and with chilling premeditation when, armed with a pistol, a rifle and a grenade launcher, he left his post twice during the night to attack civilians. He is said to have returned to base in the middle of the rampage to tell a fellow soldier: “I just shot up some people.”

Defense attorneys have argued that Bales, the father of two from Lake Tapps, Washington, was suffering from post-traumatic stress disorder and a brain injury even before his deployment to Afghanistan.

STEROIDS AND WHISKEY

Under questioning from Nance, Bales said that his use of illegal steroids, which he admitted taking to improve muscle tone and recovery time from missions, also “increased my irritability and anger.”

During a nine-day pre-trial hearing last fall, witnesses testified that Bales had been upset by a bomb blast near his outpost that severed a fellow soldier’s leg days before the shootings.

One corporal recounted that in the hours before the rampage he, Bales and a third soldier had been drinking whiskey together while watching the Hollywood film “Man on Fire,” which stars Denzel Washington as a former assassin bent on revenge.

Night-vision video footage taken from a surveillance balloon over the camp captured Bales’ arrest, showing him walking back to the post with a bed sheet or throw rug tied around his neck like a cloak as he is confronted by three soldiers who order him to drop his weapons and then take him into custody.

One of them, drinking buddy Corporal David Godwin, testified that Bales kept repeating the words, “I thought I was doing the right thing,” and, “It’s bad. It’s bad. It’s really bad.”

After Wednesday’s hearing, Scanlan told reporters her client “has been waiting for the day that he can accept responsibility for what he’s done.”

She added that Bales wanted to make a statement of apology for his actions but that Wednesday’s hearing was not the appropriate place or time.

“The forum for that is the penalty phase,” she said.

Army officials said some family members of the victims are expected to give statements at the sentencing hearing in August.

The plea deal entered on Wednesday was similar to an agreement struck at Lewis-McChord in April, when Army Sergeant John Russell pleaded guilty to killing two fellow U.S. servicemen at a military counseling center in Iraq, near Baghdad’s airport, in a 2009 shooting spree.

Russell was sentenced to life in prison without parole following an abbreviated court-martial stemming from one of the worst cases of violence by an American soldier against other U.S. troops.