State Department offering up to $10 million for information about the 2017 ambush in Niger

The U.S. Department of State is offering up to $10 million for information about the deadly 2017 attack in Tongo Tongo, Niger, which resulted in the deaths of four U.S. and four Nigerien soldiers.

Officials are looking for the identification or location of Adnan Abu Walid al-Sahrawi, who the U.S. says was the leader of the terrorist group responsible for the ambush. They say Abu Walid was the head of the organization Islamic State in the Greater Sahara (ISIS-GS), which claimed responsibility for the attack on Oct. 4, 2017, against a joint U.S.-Nigerien patrol near the village of Tongo Tongo.

The State Department is offering $5 million for information leading to Abu Walid and another $5 million for information leading to the arrest or conviction in any country of any individual who “committed, conspired to commit or aided or abetted in the commission of the 2017” attack.

Staff Sgt. Bryan C. Black, Staff Sgt. Dustin M. Wright, Staff Sgt. Jeremiah W. Johnson and Sgt. La David Johnson died during the ambush. The soldiers were accompanying a platoon of Nigerien soldiers when they were attacked by a group of about 120 ISIS-affiliated fighters close to the border with Mali.

A military investigation previously found that the mission in Niger was not approved by the proper authorities and that the soldiers there were not trained for that specific mission.

“I take ownership for all the events connected to the ambush of 4 October,” said General Thomas Waldhauser, the commander of U.S. Africa Command at a May 2018 Pentagon news conference. “Again, the responsibility is mine.”

Earlier this year, families blasted the decision to not punish higher-ranking officers in the Niger ambush after learning there would be no further disciplinary action for Army officials other than letters of reprimand.

"I don't see how people in the direct chain of command are being promoted when it was their decision to override the ground commander (who) was instrumental in my son's death,” Arnold Wright, the father of Green Beret Staff Sgt. Wright said.

ABC News' Conor Finnegan and Luis Martinez contributed to this report.