The investigation is led by the Department of Defense, but the Wall Street Journal reported on Thursday that the FBI had thrown their hat in the ring as well. Bureau officials told the WSJ that they had the authority to commandeer the probe, but had not done so. They added that their involvement in the investigation is nothing unusual.
The FBI typically handles the investigation into the deaths of American citizens overseas as well as international terror investigations. However, the Pentagon has their own in-house investigative services. In all likelihood, the FBI has been brought on to appease critics who have argued that the White House has poorly managed the aftermath of the attack.
The American and Nigerien soldiers were on a joint patrol within striking distance of the Niger-Mali border when a force of militants attacked them. Four of the twelve-odd US troops and five of the 40 Nigeriens were killed in the fighting before French gunships and a Nigerien counterattack chased the militants off.
But weeks have passed since the initial incident and very little new information has been revealed since the first couple days. The troops also lacked sufficient air and ground support, relying on allied French forces in Mali for a rescue and evacuation. Furthermore, Sgt. La David Johnson was lost in the confusion of the fighting. His body was discovered two days later.
This has led to lawmakers, most prominently Chair of the Senate Armed Services Committee Sen. John McCain (R-AZ), to demand more transparency from the White House about the attack.
"I had a better working relationship, as far as information back and forth, with [former Defense Secretary] Ash Carter than I do with an old friend of 20 years," said McCain, referring to White House National Security Adviser Lt. Gen. H.R. McMaster. "We've been waiting for weeks and weeks. We will not sit by without having a complete understanding of what's going on."
The Pentagon has insisted that they have been as forthcoming as possible with lawmakers about details regarding the attack. "The loss of our troops is under investigation," Defense Secretary James Mattis told the press on Friday. "We investigate anytime we have our troops killed, whether it be in a training accident or combat."
Mattis admitted that the Pentagon does not "have all the accurate information yet" regarding the deadly ambush, but the "US military does not leave its troops behind."
"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 added. "In this specific case, contact was considered unlikely, but there's a reason we have US Army soldiers there and not the Peace Corps, because we carry guns."
