Defense Secretary Jim Mattis speaks to U.S. troops on Wednesday at Bagram Airfield in Afghanistan. (AFP/Defense Department/Jet Fabara)

Defense Secretary Jim Mattis said Thursday that he doesn’t want the months-long investigation into how four U.S. soldiers were killed last year in Niger held up, and he expects to soon receive a memorandum about it from the Pentagon’s top general.

Mattis, speaking on a military flight home to Washington from Bahrain, said that he has been reading a draft version of the “very thick” investigation report, and that he directed people involved to get back to him by Friday evening with answers to questions he posed. He did not detail what those questions are, but his comments provide the clearest timeline yet on when the Pentagon will detail how a team of elite Special Forces soldiers partnering with Nigerien forces was effectively overrun by militants.

“I have been reading the report myself because I don’t want this dragged out,” Mattis said. “I have several questions from that as well, and hopefully I will have those answers for me.”

Marine Gen. Joseph F. Dunford Jr., chairman of the Joint Chiefs of Staff, will soon provide his endorsement of the investigation report, Mattis said. The Pentagon chief will take Dunford’s advice on it, do his own review and then “put the two together, and I will see where I’m at on that,” he said.

The Oct. 4 ambush also killed five Nigerien soldiers and has prompted scrutiny of how the soldiers were apparently diverted from a reconnaissance patrol along the Mali border to another assignment that placed them in grave danger. Nigerien officials have said the unit was asked to assist in a mission to capture or kill an Islamic State leader.

Video apparently recorded by a U.S. soldier in the fight and released by the Islamic State as propaganda shows U.S. soldiers with little cover returning fire as militants close in and shoot them. The incident has prompted U.S. Special Operations Command to review whether it should adopt a policy for U.S. troops carrying video cameras in combat, said Navy Capt. Jason Salata, a Special Operations Command spokesman. That review was first reported by Time magazine.

Killed in the hours-long firefight were Staff Sgt. Jeremiah W. Johnson, 39; Staff Sgt. Bryan C. Black, 35; Staff Sgt. Dustin M. Wright, 29; and Sgt. La David Johnson, 25. Black and Wright were elite members of the 3rd Special Forces Groups, while the other fallen soldiers were conventional service members assigned to their unit.

From left: Staff Sgt. Bryan C. Black, 35, of Puyallup, Wash.; Staff Sgt. Jeremiah W. Johnson, 39, of Springboro, Ohio; Sgt. La David Johnson, 25, of Miami Gardens, Fla.; and Staff Sgt. Dustin M. Wright, 29, of Lyons, Ga. (U.S. Army/AP)

The remains of La David Johnson were not recovered until two days later by Nigerien villagers, underscoring how chaotic the mission was for a military that prides itself on not leaving anyone behind on the battlefield. His situation trigged what the military calls a DUSTWUN, which stands for “duty status whereabouts unknown,” military officials told The Washington Post in the days after the battle. Members of the elite Joint Special Operations Command were directed to assist in the search, the officials said, though it wasn’t clear whether they participated.

The investigation was led by Army Maj. Gen. Roger L. Cloutier, the chief of staff of U.S. Africa Command. It is likely to include hundreds of pages of interviews and written witness statements from service members involved, as well as recommendations and findings for what the military might change to prevent similar incidents.

After the investigation has been approved, family members of the fallen soldiers will be briefed by the Army. Then Mattis will brief members of the media, he said.

Mattis has previously suggested that extenuating circumstances led to the difficulties in finding Johnson’s remains.

“The U.S. military does not leave its troops behind, and I would just ask you not to question the actions of the troops who were caught in the firefight and whether they did everything they could in order bring everyone out at once,” Mattis said Oct. 19.