PHOENIX -- The shooting of two U.S. Border Patrol agents near the Arizona-Mexico border may have been a case of friendly fire, a union chief for border agents and law enforcement officials said Friday.
The development could shake up the investigation into the death of one of the agents that reignited the political debate over security on the border.
George McCubbin, president of the National Border Patrol Council, a union representing about 17,000 border agents, said Friday he has learned new details from Border Patrol administrators that make him believe friendly fire could have played a part in the shooting.
"The only thing I can say is that the possibility of friendly fire is a higher likely scenario," McCubbin said, declining to elaborate on the new details.
Two law enforcement officials also told The Associated Press that the FBI is investigating the possibility that the fatal shooting of 30-year-old Agent Nicholas Ivie and the wounding of another agent early Tuesday five miles from the border was a case of friendly fire.
The probe is examining whether the two agents exchanged gunfire Tuesday in the mistaken belief that each was being fired on by a hostile gunman.
The officials spoke on condition of anonymity because the matter is under investigation.
FBI officials in Washington and Phoenix declined to comment.
Investigators trying to determine whether friendly fire occurred in a shooting involving police would compare the ballistics of officers' guns with bullet slugs that were either recovered from or passed through an officer's body, said David Klinger, a criminology professor at the University of Missouri at St. Louis and an expert in police shootings.
The officers involved in the case and any known witnesses also would be asked to provide accounts of such a shooting during interviews with investigators. And investigators would try to establish where officers and witnesses were positioned at the time of the shooting, Klinger said.
The Border Patrol couldn't immediately comment on the frequency of friendly fire incidents at the agency, but they appeared to be rare.
Neither McCubbin, who has served in the Border Patrol since 1985, nor Kent Lundgren, chairman of the National Association of Former Border Patrol Officers, had ever heard of any friendly fire incidents in the Border Patrol.
"I know of absolutely none in the past, and my past goes back to 1968," Lundgren said, citing the year he joined the Border Patrol. "I'm not saying it never happened. I'm just saying I've never heard of it."
The shooting occurred in a rugged hilly area about five miles north of the border near Bisbee, as the agents responded to an alarm that was triggered on one of the sensors that the government has installed along the border.
The wounded agent has been released from the hospital, while the third agent was uninjured.
Ivie's death marked the first fatal shooting of an agent since a deadly 2010 firefight with Mexican bandits that killed U.S. Border Patrol Agent Brian Terry in December 2010 and spawned congressional probes of a botched government gun-smuggling investigation.
Terry's shooting was later linked to that "Fast and Furious" operation, which allowed people suspected of illegally buying guns for others to walk away from gun shops with weapons, rather than be arrested.
Authorities intended to track the guns into Mexico. Two rifles found at the scene of Terry's shooting were bought by a member of the gun-smuggling ring being investigated. Critics of the operation say any shooting along the border now will raise the specter that those illegal weapons are still being used.
Twenty-six Border Patrol agents have died in the line of duty since 2002.