A Border Patrol agent who shot and killed a Mexican teenager from across the border in Arizona was acquitted Wednesday of involuntary manslaughter in a case that has drawn national attention amid heightened debate over immigration.

In 2012, the border guard, Lonnie Swartz, opened fire into the Mexican city of Nogales, killing 16-year-old José Antonio Elena Rodríguez. A jury found Mr. Swartz not guilty of second-degree murder in April but deadlocked on manslaughter charges, prompting another trial.

In court on Wednesday, the jury found Mr. Swartz not guilty of involuntary manslaughter, but it did not make a decision on voluntary manslaughter, according to court documents.

Next month, a judge from the United States District Court in Arizona will decide the status of the voluntary manslaughter charge, which the jury’s verdict left in question. In a statement, Elizabeth A. Strange, the first assistant United States attorney, said the prosecutors “fully respect” the jury’s verdict.