Federal authorities in Arizona announced they're seeking four suspects involved in the fatal shooting of Border Patrol agent Brian Terry, and the FBI offered $1 million for their capture on Tuesday.

Federal officials indicted five men in the December 2010 killing of Brian Terry, including one who is already in custody. A sixth suspect was charged with conspiracy relating to robbery, but not the killing. The indictment was unsealed in Tucson.

"Agent Terry died in the line of duty while protecting his country," United States Attorney Laura E. Duffy said. "But he was more than a federal agent—he was a son, a brother, a co-worker, and a friend to many."

The defendants, who are all Mexican nationals, allegedly entered the country to robbing drug traffickers of their contraband, when Terry and his t eam encountered them. Agent Terry was killed in a firefight that began with the agents firing bean-bag rounds, while the defenedants allegedly returned fire with AK-47 semi-automatic rifles. Two of the rifles were tracked back to the "Fast and Furious" operation.

The defendants have also been charged with assaulting three other Border Patrol agents during the Dec. 14, 2010, gunfight.

The indictment charges Manuel Osorio-Arellanes, Jesus Rosario Favela-Astorga, Ivan Soto-Barraza, Heraclio Osorio-Arellanes, and Lionel Portillo-Meza with crimes including first-degree murder, second-degree murder, conspiracy to interfere with commerce by robbery, attempted interference with commerce by robbery, use and carrying a firearm during a crime of violence, assault on a federal officer, and possession of a firearm by a prohibited person.

Rito Osorio-Arellanes, the sixth defendant, is charged with conspiracy to interfere with commerce by robbery.

Manuel Osorio-Arellanes has been in custody since his arrest the night of the shooting. Rito Osorio-Arellanes has been in custody since December 12, 2010, when he was arrested by Border Patrol agents on immigration charges.

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