SEOUL — The two-star chief of staff for U.S. Africa Command has been assigned to lead the Army’s official investigation into the ambush that led to the deaths of four U.S. soldiers earlier this month in Niger, Chairman of the Joint Chiefs of Staff Gen. Joseph Dunford said Thursday.

Maj. Gen. Roger Cloutier Jr. will lead the 15-6, as the Army’s investigation is commonly known, to answer why the 12-person U.S. Special Forces team and 30 Nigerien partnered forces ended up in an hours-long firefight with what the Pentagon suspects were Islamic State-affiliated militants.

Staff Sgt. Bryan Black, Staff Sgt. Dustin Wright, Staff Sgt. Jeremiah Johnson and Sgt. La David Johnson died in the attack.

Dunford would not say whether the troops ultimately diverted from their original tasking in order to pursue an Islamic State target. He said that as part of his review into the attack, he requested the original order that sent the troops on their Oct. 3 overnight mission. The unit was ambushed during their return to base the morning of Oct. 4.

“I read the original document that sent that patrol out, and it was a patrol to go out and identify information about the local area,” Dunford said to reporters traveling with him on a trip to Asia. “It was not targeted or focused on any specific Islamic State leader or location. Because that would have made the mission, enemy contact, more likely. The estimate at the time was enemy contact was not likely.”

“What I don’t know, and what the investigation will find out is, ‘Did they have a change of mission at any given point? If so, how did they get that change of mission? Who approved that change of mission? What was that mission?’ Those are all things that I am seeing bits and pieces of, but, honestly, I wouldn’t say any of it is fact until the investigation is complete.”

Dunford said a normal line of duty investigation takes about three to four weeks, but he expected this would take longer, given the complexity of interviewing the Nigerien, French and U.S. forces involved and determining all of the facts on the ground.

The Federal Bureau of Investigation is also looking into the incident.