Federal prosecutors on Thursday said they would not pursue another trial against a Border Patrol agent who fatally shot a Mexican teenager across a border fence but who was twice acquitted.

A filing in court shows prosecutors say they will no longer pursue the case against Lonnie Swartz, the agent who killed 16-year-old Jose Antonio Elena Rodriguez in October 2012.

"Agent Swartz is relieved and looking forward to moving on with his life without the threat of criminal prosecution hanging over his head," his attorney, Sean Chapman, said in an email to The Associated Press.

In April, Swartz was acquitted of second-degree murder, but a jury deadlocked on manslaughter charges. Prosecutors re-tried Swartz on voluntary and involuntary manslaughter charges.

They said Swartz lost his cool when he became frustrated at rock-throwers from the Mexican side of the border while on the job.

The second trial, which began in October, ended with a not guilty verdict on the involuntary charge, but the jury again deadlocked on voluntary manslaughter.

Swartz was the rare agent who was prosecuted for use of force. The shooting, and his indictment three years later, came at a time when the Border Patrol was increasingly under scrutiny for its use of force, especially pertaining to rock-throwers, or people on the Mexican side of the border who throw rocks to distract agents.

Swartz's attorney said he was acting in self-defense and following Border Patrol policy when he fired at least 16 shots at Elena Rodriguez through the slats of a border fence dividing Nogales, Ariz., and Nogales, Sonora.

Prosecutors said Elena Rodriguez was throwing rocks at Swartz and other law enforcement officers who were on scene chasing a suspected drug smuggler in an effort to distract them.

The boy's family still denies that he was involved. They say his killing was not justified.

The announcement on Nov. 21 that the jury had found Swartz not guilty on involuntary manslaughter but had deadlocked on voluntary manslaughter was met with protests from activists who marched through downtown and shut down a busy intersection.