The U.S. Border Patrol agents' union says Agent Nicholas Ivie, 30, apparently opened fire on two colleagues last week thinking they were armed smugglers. He was shot and killed when the agents returned fire.
Officials said the two sets of agents were checking out a sensor that had been activated Tuesday when they encountered each other in an area of heavy brush. Ivie apparently opened fire first and wounded one of the other agents. The wounded agent has since been released from the hospital.
Authorities said the two sets of agents knew the others were heading to the area on foot but apparently didn't know they were so close. Sensors are set up in different areas along the U.S.-Mexico border to detect smugglers or illegal immigrants, with Border Patrol agents responding when they're set off. The shooting occurred in a rugged hilly area about five miles north of the border near Bisbee, Ariz., an area known for illegal trafficking.
The new details add to an FBI statement Friday that the shooting appeared to involve no one but the agents.
Ivie's funeral is set for Monday morning. He is survived by his wife and two young daughters.
The Associated Press contributed to this report.