Correction: Earlier versions of this article about an Army investigation into the brigade commander of five soldiers accused of killing Afghan civilians misstated the brigade’s motto. This version has been corrected.

An Army investigation into the brigade commander of five soldiers accused of murdering unarmed Afghan civilians last year has concluded that he should have been relieved of duty for poor performance, but pins virtually all the blame on junior officers for failing to prevent the killings.

The administrative probe into the actions of the 5th Stryker Combat Brigade, 2nd Infantry Division, harshly criticizes Col. Harry D. Tunnell IV, the brigade commander, for defying the Army’s protect-the-population strategy in Afghanistan and instead adopting the motto “strike and destroy.”

But it stops short of holding Tunnell accountable for the alleged murders of three Afghan men, finding no “causal relation” between his aggressive leadership style and the killings.

The administrative probe, led by Brig. Gen. Stephen Twitty, was conducted separately from the Army’s criminal investigations into the killings. Twitty’s confidential report was completed in February but has been kept under seal by the Army while criminal cases proceed against more than a dozen members of the unit who have been charged with wrongdoing, including murder and drug abuse.

Details of the report were first reported Monday by the German newsmagazine Der Spiegel. The Washington Post also obtained a copy.

As a result of the investigation, Lt. Gen. Curtis M. Scaparrotti, the commander of I Corps, recommended that Tunnell receive a letter of admonition, a mark that could hamper his career in the Army but not necessarily end it.

In contrast, Army officials recommended that several junior officers — including the former platoon leader of the soldiers charged with murder — receive letters of reprimand, a more serious punishment.

The Army declined to comment on the report or the results of the investigation into Tunnell’s leadership, citing the ongoing criminal cases. “Public discussions of [the] investigation findings is inappropriate and could affect the outcome of these cases,” Maj. Christopher Ophardt, a spokesman for I Corps, said in a statement. I Corps is based at Joint Base Lewis-McChord, near Tacoma, Wash.

Tunnell also declined to comment through a spokeswoman for the Army’s Accession Command at Fort Knox, Ky., where he was reassigned after his brigade returned from Afghanistan in July 2010.

Although it does not admonish Tunnell for the alleged misconduct by his soldiers, the report provides a blistering portrayal of his performance during his brigade’s year-long deployment to Afghanistan.

Generals whom Tunnell had served under while in Afghanistan said that they had lost confidence in his ability to lead and that he constantly butted heads with superiors, especially British Maj. Gen. Nick Carter, the then-commander of allied forces in southern Afghanistan.

In particular, the report found, Tunnell mocked the doctrine of counterinsurgency, under which U.S. and NATO forces attempted to win the loyalty of Afghans by protecting civilians from the Taliban. Instead, Tunnell advocated for an old-fashioned “counterguerrilla” strategy, in which he instructed his soldiers to concentrate on engaging and destroying the enemy.

“Looking back on my relationship with him, I regret that I wasn’t more involved in his professional development during his tenure as a brigade commander,” said Brig. Gen. Frederick B. Hodges, then-director of operations in southern Afghanistan, according to the report. “I should have specifically told him that MG Carter and I had lost confidence in his ability to command from his failure to follow instructions and intent.”

The report also found that Tunnell’s disdain for counterinsurgency was apparent well before the Stryker brigade went to Afghanistan. Commanders at the Army’s National Training Center at Fort Irwin, Calif., nearly failed to certify Tunnell’s brigade as ready to deploy because of his resistance to the counterinsurgency doctrine.

“The unit leadership was unable to adjust its mindset,” Brig. Gen. Randy Dragon, who was the operations group commander at the National Training Center, said in a statement for the report.

Tunnell has remained resolutely opposed to counterinsurgency, even in the aftermath of the killings and the subsequent investigations, which have amounted to one of the biggest scandals facing the Army from the war in Afghanistan.

In his own statement to investigators in November, Tunnell described counterinsurgency as a colossal mistake.

“Soldiers lives are routinely put at hazard because the doctrine has not been written within a context of American military art and science, organization or capability,” he wrote. “US Army forces are not organized, trained, or equipped to implement the doctrine.”

The report concluded that criminal misconduct in the brigade was confined largely to a single platoon. In addition to being charged with the murder of three unarmed Afghan civilians between January and May 2010, soldiers from the platoon have been charged with hoarding body parts and posing for photographs next to their victims.

Twitty’s investigation cited an “alarming” lack of discipline in the platoon. He found that at least 15 members regularly smoked hashish, including in their Stryker combat vehicle.

He also reported that soldiers killed chickens and dogs for sport, and that one platoon member negligently fired a grenade launcher, destroying a protective barrier at his forward operating base.

On another occasion, the entire platoon fell asleep while on patrol, failing to post anyone on guard watch, the report found. Soldiers also regularly scrawled the word “Crusader” on portable bridges over Afghan irrigation ditches.