The body of Sgt. La David Johnson was found nearly a mile from the scene of the ambush in Niger that left Johnson and three other U.S. soldiers dead, CNN reported Friday.

The report comes two weeks after roughly a dozen U.S. soldiers and 40 Nigerian troops were ambushed by Islamic militants during a joint patrol in the northwest African country.

Johnson's body was found 48 hours after troops realized he was missing, sparking questions from lawmakers and military officials as to why Johnson was left behind.

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Defense Secretary James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE confirmed on Thursday that the Pentagon had launched a formal investigation into the incident.

"The loss of our troops is under investigation," Mattis told reporters. "We investigate anytime we have our troops killed, whether it be in a training accident or combat."

"These terrorists are conducting war on innocent people of all religions, they are conducting war on innocent people who have no way to defend themselves," he continued.

"In this specific case, contact was considered unlikely, but there's a reason we have U.S. Army soldiers there and not the Peace Corps, because we carry guns."

Mattis also looked to express the military's commitment to the safety and wellbeing of soldiers in harm's way.

"We honor our troops. Everyone of them. Every life is critical. These young people look past the hot political rhetoric and sign up to volunteer for the armed forces," he said.

The FBI has also joined the investigation into the ambush.

However, various lawmakers, most notably Sen. John McCain John Sidney McCainMomentum growing among Republicans for Supreme Court vote before Election Day McConnell urges GOP senators to 'keep your powder dry' on Supreme Court vacancy McSally says current Senate should vote on Trump nominee MORE (R-Ariz.), have demanded answers as to what went wrong while the soldiers were on patrol.

McCain raised the possibility on Thursday of issuing a subpoena as a means to get answers from the Trump administration about the attack.

Mattis met Friday with McCain on Capitol Hill. The two affirmed their respect for one another afterward, with McCain saying he and Mattis were working on “clearing up” the lack of information.