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

Maj. Gen. Roger Cloutier, U.S. Africa Command’s chief of staff, is spearheading the investigation team, which will be traveling to areas in the U.S., Africa, and Europe to gather information, according to a statement from the Pentagon on Wednesday.

Although the investigation is anticipated to conclude by January, families will be notified if additional time is necessary.

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 reportedly gathering intelligence information concerning a terrorist leader when they were ambushed by Islamic State-linked fighters on Oct. 4, according to a CNN report.

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 to ask questions about the ambush amid criticism from lawmakers concerning the transparency from the Pentagon about the attack.

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.