(CNN) -- A U.S. Border Patrol agent believed killed in a friendly fire shooting near the Arizona-Mexico border died of a gunshot wound to the head, an autopsy report revealed.

The report released Wednesday by the Pima County Medical Examiner's office determined Nicholas J. Ivie, 30, of Provo, Utah, died from what was described as a "penetrating gunshot wound of the head involving the brain."

Ivie was killed and another agent was wounded on October 2 in a shootout near Naco, Arizona, after responding to a sensor that had gone off near the border, according to U.S. Customs and Border Enforcement.

The FBI has said there are strong indications in its preliminary investigation that Ivie was killed as a result of an accidental shooting that involved only Border Patrol agents.

At the time, a law enforcement official said investigators at the scene found only shell casings believed to have been fired by the Border Patrol agents.

Ivie was killed near a border station recently named for Brian Terry, whose 2010 death led to the public disclosure of the botched Fast and Furious gun-smuggling sting.

Ivie was the 14th agent killed in the line of duty since 2008, including three this year.

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