TUCSON, Ariz. (AP) — A rock-throwing teenager didn't deserve to die when a U.S. Border Patrol Agent hit him with 10 shots as he stood on a street on the Mexican side of the border, prosecutors said Wednesday at the start of murder trial of the federal officer who contends he fired because he was in danger.

Assistant U.S. Attorney Mary Sue Feldmeier acknowledged in opening statements that Jose Antonio Elena Rodriguez was throwing rocks over the fence to help drug smugglers by serving as a distraction as they returned to Mexico after leaving backpacks of marijuana in the U.S.

But she said the teen didn't deserve the death penalty for his crime and agent Lonnie Swartz "became the judge, the jury and the executioner" when he killed the 16-year-old in 2012.

Swartz has pleaded not guilty to second-degree murder.

Civil rights attorneys say the trial in U.S. District Court before Judge Raner C. Collins appears to be the first Justice Department prosecution of a Border Patrol agent in a deadly shooting across the international boundary.

It comes amid President Donald Trump's campaign for a wall along the 2,000-mile (3,200-kilometer) U.S.-Mexico border and his crackdown on illegal immigration.

Defense attorney Sean Chapman told the jury Swartz was protecting himself and other agents when he fired across the border and Rodriguez put himself in danger by throwing rocks at the officers.

Rocks, including some larger than baseballs, were thrown by several people in Nogales, Mexico into Nogales, Arizona and hit another agent in the foot and also struck a police dog, according to Chapman.

"This is not a game, this is serious, this is dangerous," Chapman said. "There was a real risk that Lonnie Swartz faced that night. Rocks kill. Rocks maim. Rocks can crack a skull or take an eye out or break a bone."

Prosecutors say Swartz opened fire at about 11:30 p.m. on Oct. 10, 2012, through metal poles of a 20-foot (6-meter) fence that sits on a 25-foot (about 7.6-meter) embankment above Mexico's Calle Internacional, a street lined with homes and small businesses.

An autopsy showed the unarmed teen was shot 10 times. The prosecutor said the teenager was struck eight times in the back and twice in the head.

Swartz is on administrative leave pending the outcome of the trial. The agency has not said if he is continuing to receive his salary.

Chapman said after the shooting the agent vomited, then wept.

About 20,000 people live on the Arizona side and about 300,000 live on the Mexico side, but the two communities linked by family members, trade and culture have long been referred to locally as "Ambos Nogales" — "Both Nogales" in Spanish.