Sgt. La David Johnson, one of the four American soldiers killed in the ambush in Niger last month, may have been captured and then executed, a report published Friday evening said.

Adamou Boubacar, a farmer and trader from the Nigerien town of Tongo Tongo, said children who were tending cattle notified him that they had found the Johnson’s remains on Oct. 6, just two days after the attack, according to the Washington Post.

Boubacar said he went to the bushy area approximately a mile away from the location of the attack and found Johnson’s body face down. Boubacar said the back of his head had been smashed, possibly from a bullet. His hands were bound with rope, suggesting Johnson had been captured.

Nigerian military sources said last week they think fighters linked to the Islamic State decided to capture and kidnap Johnson, according to a CBS News report.

The Pentagon has not disclosed how Sgt. La David Johnson, who was found two days later about a half mile away from the ambush, was separated from other soldiers.

Their team and a partner force of 30 Nigeriens were gathering intelligence information concerning a terrorist leader when they were ambushed by Islamic State-linked fighters on Oct. 4, CNN reported.

The soldiers were attacked as they were returning to their operating base following a visit to a village, Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff, said last month. He added that air support had been requested approximately an hour after the attack and probably hadn't been requested earlier because soldiers thought they didn't need it.

Senate Armed Services Committee Chairman John McCain, R-Ariz., met with Defense Secretary Jim Mattis last month to ask questions about the ambush amid criticism from lawmakers concerning the transparency from the Pentagon about the attack.

The U.S. Army has notified the family members of the four U.S. soldier killed that the investigation of the incident will likely conclude in January 2018.

The U.S. has approximately 800 troops in Niger and 6,000 conducting missions throughout Africa. At least 20 Americans have lost their lives serving the nation since January.