The murder trial of a U.S. Border Patrol agent accused of shooting across the international boundary into Mexico in 2012 and killing a teenager started with jury selection Tuesday in U.S. District Court in Tucson.

Lonnie Swartz has pleaded not guilty to second-degree murder in the killing of 16-year-old Jose Antonio Elena Rodriguez. The teenager was on a street in Nogales, in the Mexican state of Sonora, just across the border from Nogales, Arizona, the Associated Press reports.

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

Swartz's lawyers have said Elena Rodriguez threw rocks just before he was shot in an attempt to create a distraction for drug smugglers and that the officer was justified in using lethal force. They have requested that jurors visit the site at night to experience the area after dark.

The U.S. Attorney's office has said it won't dispute that the boy was throwing rocks, but it's unknown if he had any link to drug smugglers. They argue an unreasonable amount of force was used.