"We weren't worried when we set out. We were a little scared of the Taliban, but not of government forces," he said referring to the Afghan national army and its U.S. allies. "Why would they attack us?"

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American aircraft began tracking the vehicles at 5 a.m.

The crew of an AC-130, a U.S. ground attack plane flying in the area, spotted a pickup and a sport utility vehicle with a roof rack converge from different directions.

At 5:08 a.m., they saw one of the drivers flash his headlights in the darkness.

The AC-130 radioed the Predator crew in Nevada: "It appears the two vehicles are flashing lights, signaling."

With that, the travelers became targets of suspicion.

At Creech Air Force Base, 35 miles northwest of Las Vegas, it was 4:30 p.m., nearly dinner time.

A few hours earlier, a dozen U.S. special operations soldiers, known as an A-Team, had been dropped off by helicopter near Khod, five miles south of the convoy. The elite unit was moving on foot toward the village, with orders to search for insurgents and weapons.

Another U.S. special operations unit had been attacked in the district a year earlier, and a soldier had been killed. This time the AC-130, the Predator drone and two Kiowa attack helicopters were in the area to protect the A-Team.

The Predator's two-man team — a pilot and a camera operator — was one of the Air Force's most-experienced. The pilot, who had flown C-130 cargo planes, switched to drones after 2001 and had spent more than 1,000 hours training other Predator pilots. (The Air Force declined to name the crew or make them available for interviews.)

Also stationed at Creech were the Predator's mission intelligence coordinator and a safety observer.

In addition, a team of "screeners" — enlisted personnel trained in video analysis — was on duty at Air Force special operations headquarters in Okaloosa, Fla. They sat in a large room with high-definition televisions showing live feeds from drones flying over Afghanistan. The screeners were sending instant messages to the drone crew, observations that were then relayed by radio to the A-Team.

On the ground, the A-Team was led by an Army captain, a veteran of multiple tours in Afghanistan. Under U.S. military rules, the captain, as the ground force commander, was responsible for deciding whether to order an airstrike.

At 5:14 a.m., six minutes after the two Afghan vehicles flashed their lights, the AC-130 crew asked the A-team what it wanted to do about the suspicious vehicles.

"Roger, ground force commander's intent is to destroy the vehicles and the personnel," came the unit's reply.

To use deadly force, the commander would first have to make a "positive identification" that the adversary was carrying weapons and posed an "imminent threat."

For the next 4 1/2 hours, the Predator crew and the screeners scrutinized the convoy's every move, looking for evidence to support such a decision.

"We all had it in our head, 'Hey, why do you have 20 military age males at 5 a.m. collecting each other?' " an Army officer involved in the incident would say later. "There can be only one reason, and that's because we've put [U.S. troops] in the area."

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