EL PASO, Texas (Border Report) — A Border Patrol precision marksman shot and killed a gunman who was robbing a group of migrants and was threatening to shoot one of them on Sunday in the mountains east of San Diego, U.S. Customs and Border Protection said.

According to a CBP news release issued Thursday, agents from the U.S. Border Patrol Tactical Unit, or BORTAC, were patrolling near the Puebla Tree area of the Otay Mountains, approximately 5 miles east of the Otay Mesa Port of Entry, where migrants often are assaulted and robbed.

Migrants told investigators that they were walking along a paved road early in the morning when they were approached by four men, at least one of whom had a gun.

CBP said one BORTAC team was hiding in a ravine about 70 yards away, and another BORTAC agents, including the precision marksman, were positioned on high ground approximately 275 yards away.

Both BORTAC teams described similar events.

They said the armed individual demanded money from the group, racked his pistol to chamber a round, and pointed the weapon at one of the migrants.

That’s when a single shot rang out and the gunman fell to the ground, CBP said.

Witnesses told investigators that they had no idea where the shot came from.

CBP confirmed that the BORTAC precision marksman fired one round, striking the armed individual, and that no other injuries were reported.

The shooting happened just before 7 a.m. Sunday. Border Patrol and local emergency crews responded and tended to the alleged gunman.

The man, who was only identified as a Mexican national, was pronounced dead at 8:14 a.m.

CBP said agents found a handgun next to the individual. Agents also arrested 17 migrants who were in the area. They said three other individuals who were believed to be armed ran back into Mexico.

According to the CBP news release, the San Diego County Sheriff’s Department, the Federal Bureau of Investigation, and CBP’s Office of Professional Responsibility are currently investigating this incident. CBP’s National Use of Force Review Board will review this incident when the investigation is complete. The Department of Homeland Security’s Office of Inspector General has been notified.

CBP said video from the agents’ body cameras will be released when it is deemed appropriate and it is determined that it won’t compromise the investigation.