A Pakistani militiaman who shot to death a U.S. Army officer in a 2007 ambush near a Pakistani border town apparently acted alone and not as part of a coordinated Pakistani army plot, according to investigation details released Monday by the Pentagon.

Army Maj. Larry J. Bauguess, Jr., was gunned down as he and other U.S. officers were headed toward helicopters that would take them back across the border following a meeting with Afghan and Pakistani officers in the frontier town of Teri Mengel. The meeting was meant to calm tensions along the border.

In reporting Bauguess's death on May 15, 2007, one day after the incident, the U.S. military said he died of wounds sustained from "enemy small arms fire," without mentioning that the gunman was Pakistani. Pakistan is a U.S. counterterrorism ally and receives billions in aid from Washington, but relations are badly strained.

Pakistan has resisted strong U.S. pressure to expand its military counterterrorism operations to include areas and militants that pose a direct threat to U.S. soldiers in Afghanistan.

The Army investigation conducted in the days following the attack was withheld from public release until Monday, when declassified excerpts from an executive summary were released.

The probe said none of the other Americans with Bauguess at the time could have done anything to prevent the killing. No follow-up U.S. investigation was done, according to the U.S. Central Command.

Pakistani authorities suggested at the time that the soldier acted alone or in concert with a small number of individuals.

It is unclear from the U.S. investigation report whether the gunman was killed in an ensuing exchange of gunfire with U.S. soldiers.

For years, Washington sought to play down any signs of duplicity by Pakistan, whose provision _ or at least tolerance _ of havens on its side of the border is widely seen as aiding the Taliban and other militants who are fighting and killing American and Afghan forces in Afghanistan.

The May 2007 killing of Bauguess raised tough questions about Pakistani motives. A September 2011 New York Times report, based on interviews with Afghan and Americans officers who were at the scene, portrayed the attack as a deliberate, planned assault by Pakistan, possibly as an act of revenge.

But excerpts from the U.S. Army investigation discount the notion of a Pakistani conspiracy. It said the man who shot Bauguess with an AK-47 was wearing the uniform of a local militia, known as the Kurram militia, which is part of the larger Frontier Corps. The militia reports to the Pakistani army.

"This appears to have been a premeditated event on the part of the initial shooter," the report said. "There is little evidence to support collaboration within the Pakistani militia or military. Based upon this finding, there is little the coalition forces could have done to prevent the ambush."

Bauguess, 36, of Moravian Falls, N.C., was assigned to the 4th Brigade of the 82nd Airborne Division.

He was among a group of American officers who attended what is known as a Border Flag meeting to discuss with Afghan and Pakistani officers how to tamp down tensions and lessen fighting along the border.

"There were no indications of hostile intent or suspicious activity before, during or immediately following" the talks "that would have led to a heightened security posture on the part of the coalition forces," the report said.

After the meeting, the Americans were getting into vehicles for a short drive to their helicopters when the lone gunman standing 8 to 10 feet from Bauguess's vehicle launched a burst of automatic gunfire.

One of the Americans in the bed of a pickup truck leaped to the ground and returned fire. That precipitated a "sporadic engagement" of fire between U.S. and Pakistani personnel for about 10 minutes. As many as seven Pakistanis were killed.

The report concludes that the Pakistanis who fired on the Americans after the killing of Bauguess were reacting to the U.S. shots and were not in concert with the gunman.

Although the U.S. government had not previously revealed any details of its investigation, the top U.S. commander in Afghanistan at the time, Army Gen. Daniel McNeill, briefly mentioned the attack in a June 2008 interview with Pentagon reporters. He called Bauguess's death an "assassination" and he said the killer was himself "immediately shot down" by an American soldier.

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Robert Burns can be reached on Twitter at http://twitter.com/robertburnsAP