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.