TUCSON — A U.S. Border Patrol agent died Sunday after responding to a triggered sensor at a remote part of the Arizona border east of Nogales, the Tucson Sector chief said.

Roy Villareal, the chief patrol agent, told reporters that Agent Robert Hotten, 44, was working with two other border agents on Sunday afternoon, responding to what appeared to be a group of migrants who had activated a ground sensor near Mount Washington, south of Patagonia at the Coronado National Forest.

After several hours of trying to contact him on the radio with no response, the agents began to search for Hotten in that area, finding him unconscious at about 4:15 p.m., Villareal said.

"When Agent Hotten was found unresponsive, it appears that he had fallen and may have hit his head on some rocks, but again at this stage we don't know that was the cause of death," he said during a Monday afternoon news conference in Tucson.

Agents immediately began providing first aid, but they were hampered by the mountainous terrain where they found Hotten, Villareal said.

Villareal described their actions as a "heroic effort."

Responding agents performed CPR on Hotten for nearly two hours before deciding to carry him on foot for nearly a quarter of mile. It took almost 25 minutes to reach the point where he could be airlifted.

Hotten was transported to a hospital in Nogales, where doctors pronounced him dead on Sunday night.

Villareal said the FBI was investigating Hotten's death. Even though the agency had initially ruled out foul play, the chief said that "because we cannot rule out foul play or this being an accident, the FBI has opted to take the lead."

Hotten was responding to the triggered sensor by himself, as is customary for border agents, the agency said.

Villareal added that they believe the group of about seven migrants had activated the ground sensor near Mount Washington just after 1 p.m. Sunday.

"One individual was arrested. That person is currently being detained and pending an interview with the FBI," he added.

Hotten had been with the Border Patrol since 2009. He was assigned to the Sonoita station, where agents are responsible for patrolling the mountain areas east of Nogales.

He's the 14th agent from the Tucson Sector who has died or was killed in the line of duty, according to the sector.

He is survived by his wife, son, mother and brother.

Mark Morgan, the acting CBP commissioner, sent out a tweet Monday disclosing the agent's death.

"My thoughts and prayers are with his wife, son, loved ones, and colleagues," he wrote.

Have any news tips or story ideas about the U.S.-Mexico border? Reach the reporter at rafael.carranza@arizonarepublic.com, or follow him on Twitter at @RafaelCarranza.

Support local journalism. Subscribe to azcentral.com today.