In this August 2011 image, Staff Sgt. Robert Bales participates in an exercise at the National Training Center at Fort Irwin, Calif. (Spc. Ryan Hallock/Associated Press)

U.S. military commanders missed signs that Army Staff Sgt. Robert Bales “would engage in future unwarranted violent behavior against Afghans,” according to an Army investigation of a 2012 massacre in which Bales left a remote base and shot 22 villagers.

The report, which U.S. Central Command released Tuesday after refusing to do so for three years, concluded that the command climate at the base “suffered from low standards of personal conduct and discipline.” But it also said that concerns about Bales’s conduct “did not rise to the level of warnings or indicators” that he was planning a shooting rampage, which was among the worst atrocities of the war.

Bales, 42, is serving a life sentence after he pleaded guilty to murdering 16 people, mostly women and children, and burning many of their bodies during a middle-of-the-night attack that sparked widespread protests in Afghanistan and led to a temporary suspension of combat operations.

The report offers no explanation for why Bales sneaked away to kill the villagers or any insight into his mental and medical assessments before his deployment.

Days before the attack, Bales had beaten an Afghan truck driver and acted erratically at the base while on steroids, the report said. But that behavior alone did not suggest that he would “commit the extremely violent acts” of March 2012, the report said.

Non-commissioned officers, not higher-ups, were to blame for not curbing drinking and steroid use, the investigation found.

Although acknowledging those deficiencies at the small site, the report explicitly states that command issues did not figure into the shootings.

“Command climate issues had no effect or contribution whatsoever” to Bales’s rampage, the report says. After the shootings, one Special Forces member was discharged for giving Bales steroids and a soldier was disciplined for drinking alcohol.

Bales was on his fourth deployment in 10 years after three tours in Iraq. The married father of two was a squad leader with a Stryker brigade based at Joint Base Lewis-McChord near Tacoma, Wash., and was working with a small team that included Special Forces in Kandahar province.

Army Reserve Maj. Gen. Ricky L. Waddell, the report’s lead investigator, wrote that he had limited his inquiry to search for previous warning signs in Bales’s conduct because of the then-pending criminal investigation and military proceedings. Waddell said his review of Bales’s medical and mental health records was limited.

The investigation started within two weeks of the shootings, ran for a month and was forwarded to CentCom in June 2012, about a year before Bales’s 2013 guilty pleas.

When he pleaded guilty, Bales admitted that while deployed he used sleeping pills, steroids and liquor — including drinking whiskey in the hours before he twice sneaked away from his post on March 11, 2012, to walk to two villages. Bales went door to door before shooting 22 people. He burned bodies using kerosene from a lamp, testimony showed.

Bales had left his camp before dawn, killing some villagers, then returned to his base and woke a fellow soldier, telling him he had shot people, that soldier recounted in court. The statement — which amounted to a confession — seemed so preposterous that the soldier said he did not believe Bales and went back to sleep, he told the court.

Bales left the post a second time and killed the rest of his victims in another nearby village. He returned to the base in a blood-stained uniform and wearing sheeting torn from a doorway that he had fashioned into a cape.

Marine Corps Gen. John R. Allen, who was commander of U.S. and NATO forces in Afghanistan at the time of Bales’s actions but has since retired, commissioned the investigation.

In accepting the report, Allen wrote, “I want to express my heartfelt sorrow” and extended his condolences to the families and friends of the villagers. He also pledged tighter discipline and urged better training of conventional forces, such as Bales and others on the base, who are selected to work in villages to stabilize them and counter insurgents.

“Though words and investigations cannot undo what happened, please be assured that I will continue to take every measure to ensure that our forces are well disciplined and follow the laws of armed conflict,” Allen wrote.

After the shootings, a commander at Bales’s outpost warned soldiers to get rid of alcohol and hide contraband because Army investigators were on their way, according to the report. Some military members also lacked credibility in their accounts of events and some Special Forces members showed “disdain” for infantry units and more loyalty to one another than to Army values, the investigation found.

The report on Bales — known as an Army 15-6 report— was withheld as Bales’s criminal case progressed but finally was released after repeated media requests, including from The Washington Post, under the Freedom of Information Act.

The nearly 600-page document contains numerous recommendations, including more explicit training on personal conduct and discipline and acceptable behavior toward local residents. It advised keeping the small base camp open because removing it would “give the enemy an unearned propaganda victory.”

The report also called for closer contact between commanders at in-country headquarters and remote sites.

In addition, the document exposed a gap between senior soldiers who either did not know of banned behavior, including drinking, at the base or participated in it, while junior soldiers felt uncomfortable “jumping the chain” to report violations.

During Bales’s military hearing, a comrade at the outpost testified that Bales showed no remorse when he was taken into custody.

Bales himself offered no explanation when he pleaded guilty and the judge asked him why he had shot. “I’ve asked that question a million times, and there is not a good reason in the world for the horrible things I did,” Bales replied.

Bales later sought clemency, but was denied, in a long letter to Army officials in which he said he had become “paranoid and ineffective” by the time of his Afghan deployment and filled with hate “towards everyone who isn’t American.” The letter was obtained by the News Tribune of Tacoma in June, after Bales’s conviction had been upheld.

Bales also wrote in the letter that during his imprisonment at Fort Leavenworth in Kansas, he has come to see that “what I thought was normal was the farthest thing from normal.”

Bales had financial problems related to loans on his home, was arguing with his wife while deployed and had not received a promotion he had expected, according to testimony. Bales enlisted in 2001 and was living in Lake Tapps near the Tacoma base.

He had been on his remote base for 89 days before the shootings.