Funeral of Border Patrol agent Robert Rosas

A Border Patrol honor guard stands at attention and salutes before agent Robert Rosas' flag-draped coffin during a memorial in El Centro for the fallen agent in 2009. Three of his killers have now been sentenced to prison. (Don Bartletti / Los Angeles Times / July 31, 2009)

A third defendant in the robbery and killing of Border Patrol agent Robert Rosas was sentenced Thursday to a lengthy term in federal prison.

Jose Luis Ramirez-Dorantes, 46, a Mexican national, was sentenced in San Diego federal court to 55 years in prison for the July 2009 ambush killing near Campo in southern San Diego County.

Two other defendants, Marcos Rodriguez-Perez and Christian Daniel Castro-Alvarez, were earlier sentenced to 56 years and 40 years, respectively.

“We hope that in some small way, these successful prosecutions can make a difference to members of the Rosas family who have suffered such a tragic, irreparable loss,” said U.S. Atty. Laura Duffy.

A fourth defendant, Emilio Samyn Gonzales-Arenazas, has pleaded guilty and is  awaiting sentencing.

A fifth suspect, Juan Chacon-Morales, is a fugitive. The FBI is offering a reward of up to $100,000 for information leading to his arrest.

The five -- all of whom, prosecutors said, were crossing into the U.S. illegally -- are accused of detaining Rosas at gunpoint, shooting him multiple times and then stealing his weapon, night-vision device and other equipment before fleeing back to Mexico.

Rosas, 30, had been with the Border Patrol for three years. He was survived by a wife, son and daughter.

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tony.perry@latimes.com