TUCSON, Ariz. (Reuters) - A U.S. Border Patrol agent was acquitted of involuntary manslaughter on Wednesday in the shooting death of a Mexican teenager through a border fence, marking another defeat for federal prosecutors in the second trial over the 2012 killing.

FILE PHOTO: U.S. pro-migration activists hold candles and pictures of late Mexican youth Jose Antonio Elena Rodriguez through the border fence between Mexico and the U.S. in Nogales October 10, 2013. REUTERS/Alonso Castillo

Lonnie Swartz, 43, was acquitted by a federal jury in Tucson after two days of deliberations in the death of 16-year-old Jose Antonio Elena Rodriguez.

Swartz had been acquitted of a second-degree murder charge in April, but the jury remained deadlocked on two other charges, requiring a second trial that began in October.

Jurors on Wednesday refused to make a decision on the higher charge of voluntary manslaughter against Swartz, opening the possibility prosecutors could pursue that charge in a third trial.

Outside of the court, the boy’s family said they would continue to push their case by pursuing a civil lawsuit and by asking the Mexican government to intervene.

Swartz was standing on an embankment about 14 feet (4.27 m)above Elena Rodriguez and behind the 22-foot-high metal fence that separates Nogales, Arizona, from Nogales, Sonora, when he fired 16 shots in 34 seconds, hitting Elena Rodriguez 10 times in the back and head. Swartz said he fired in self-defense after rocks were thrown at him and other agents.

The trial was a rare prosecution against a U.S. Border Patrol agent for using deadly force. The last such case in 2008 ended with the dismissal of charges.

Wednesday’s verdict came as President Donald Trump was considering giving U.S. troops authority to protect immigration agents stationed along the U.S. border with Mexico if they come under threat from migrants seeking to cross into the United States.

Trump made his hard-line policies toward immigration a key issue ahead of midterm elections earlier this month.

Swartz has been on leave without pay from the Border Patrol while facing the criminal charges.