A mistrial was declared Monday in the case of a U.S. Border Patrol agent after an Arizona jury acquitted him of a second-degree murder charge in the death of a teen from Mexico but deadlocked on lesser counts of manslaughter.

The decision by U.S. District Judge Raner Collins means prosecutors could seek another trial for Agent Lonnie Swartz on the manslaughter charges in the 2012 death of Jose Antonio Elena Rodriguez, who was fatally shot as he threw rocks at authorities during a drug smuggling attempt. Prosecutors say they were evaluating whether to pursue a retrial, reports the Associated Press.

Jurors had deliberated about 18 hours over five days in what human rights attorneys say was the first prosecution of a Border Patrol agent in a fatal shooting across the border.

Swartz fired 16 shots late on Oct. 10, 2012, through a 20-foot fence that sits on an embankment above Mexico's Calle Internacional, a Nogales street lined with homes and small businesses.

Prosecutors acknowledged during the monthlong trial that Elena Rodriguez was lobbing rocks across the border during a drug smuggling attempt.