TUCSON, Ariz. (AP) — Closing arguments began Monday in the second-degree murder trial of a U.S. Border Patrol agent accused of shooting across the border into Mexico and killing a teenager five years ago.

The agent, Lonnie Swartz, is accused of killing 16-year-old Jose Antonio Elena Rodriguez in a rare Justice Department prosecution of a federal agent in a fatal cross-border shooting.

Since the nearly one-month trial began March 20, prosecutors have acknowledged that the teen was throwing rocks from Nogales, in the Mexican state of Sonora, across the border during a drug smuggling attempt.

But they have said Elena Rodriguez did not deserve to die for rock throwing and argued that Swartz used an unreasonable amount of force.

Defense attorneys say Swartz fired to protect himself, other border agents and police officers on the U.S. side in Nogales, Arizona. They have said the agent was justified in using lethal force.

An autopsy showed the unarmed teen was shot 10 times, eight times in the back and twice in the head.

The trial in U.S. District Court in Tucson comes as President Donald Trump has called for National Guard troops to head to the border to free up Border Patrol agents to concentrate on stopping drugs and people from illegally coming into the United States. Trump's crackdown on immigration and his pledge to build a "big, beautiful wall" along the 2,000-mile (3,200-kilometer) U.S.-Mexico boundary have been a cornerstone of his presidency.

The 2012 killing was felt deeply in the twin communities of Nogales, with about 20,000 people living on the Arizona side and about 300,000 on the Mexico side. The communities are linked by family members, trade and culture and have long been referred to locally as "Ambos Nogales" — "Both Nogales" in Spanish.

Swartz opened fire late 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 Mexico's Calle Internacional, a street lined with homes and small businesses.

During the trial, jurors quietly visited at night under a request by defense attorneys that they have the opportunity to experience the area after dark to get a better idea of what Swartz was facing.

The agent, who is on administrative leave pending the trial's outcome, took the stand but testified that he remembered little of what happened.

Swartz pleaded not guilty after being indicted by a federal grand jury in 2015 and is free on his own recognizance. The Border Patrol has not said if he is receiving his salary.

Prosecutors and defense attorneys have declined to comment while the trial is ongoing.

Lee Gelernt, a New York-based lawyer with the American Civil Liberties Union, has said he believes Swartz will be the first border agent prosecuted by the Justice Department in a fatal shooting across the international line.

Gelernt is handling a parallel civil case, now before the 9th U.S. Circuit Court of Appeals in San Francisco, which the teen's mother filed against Swartz seeking monetary damages.

The lawsuit argues that Elena Rodriguez was protected by U.S. constitutional guarantees for due process when he was shot dead in Mexico because the twin towns of Nogales are part of a unique cross-border community.