CBS News has learned one of the four American soldiers killed in the ambush in Niger may have been kidnapped by Islamic militants who opened fire on a group of U.S. and Nigerien troops in early October.

The Pentagon has not said how Sgt. La David Johnson became separated from the other soldiers.

Hundreds of bullet casings and bushes stained with blood are evidence of just how intense the fighting was at the site where the group of American and Nigerien soldiers came under heavy fire.

Terrified villagers said the battled raged on for more than two hours.

The troops had stopped for supplies in the village of Tongo Tongo when heavily armed attackers appeared on motorbikes and started shooting.

CBS News

Initially, a few fighters from a group linked to the Islamic State of Iraq and Syria (ISIS) drew the troops to this spot. They burnt down that school and then pushed them in this direction to where the ambush actually took place.

When it was over, village elder Adamou Bububaker said he saw three U.S. soldiers slumped dead in their truck.

"Two of the bodies were in the vehicle and another on the ground," he said. They had been stripped of their uniforms.

But Johnson's body was found two days later, about a half a mile away. Nigerien military sources tell CBS News they believe ISIS fighters decided to try and kidnap Johnson.

The fighters later shot him and dumped his body in the bushes, his hands roped together.

Nigerien military sources insist the mission was to capture a terrorist leader and not focused on reconnaissance, as the Pentagon has stated. Either way, the soldiers had been instructed to stay overnight in territory where more than a dozen extremist groups are operating.

Asked if they were taking too big of a risk, one Nigerien soldier would only answer if we did not show his face.

"Do you think you were taking too big a risk?" Patta asks.

"The Americans? Yes, they took a risk," the soldier says.