An Arizona jury on Wednesday acquitted a United States Border Patrol agent of involuntary manslaughter in the killing of a Mexican teen through a border fence, sparking a protest in downtown Tucson following another loss for federal prosecutors in the second trial over the 2012 killing.

Jurors in Tucson found Lonnie Swartz not guilty of involuntary manslaughter but didn’t come to a decision on voluntary manslaughter. The verdict comes months after Swartz was acquitted of second-degree murder by another jury that had deadlocked on manslaughter charges, allowing prosecutors to pursue the case again.

Border Patrol agents are rarely criminally charged for using force. But the killing of 16-year-old Jose Antonio Elena Rodriguez sparked outrage on both sides of the border and it came at a time when the agency was increasingly scrutinised for its use of force.

Outside the court on Wednesday, a small group of activists protested the verdict, and one man was detained, local media outlets reported.

The protest grew later in the day as scores of demonstrators shut down an intersection, snarling traffic in downtown and prompting authorities to briefly close several freeway ramps.

Family of Jose Antonio Elena Rodriguez, killed by @cbp agent Lonnie Swartz in cross border shooting 2012. If the agent returns to work he will kill again—- mother. pic.twitter.com/GnD8w9oaXm — Michel Marizco (@BorderReporter) November 21, 2018

One sign protesters carried said, “Abolish Border Patrol”, while another read, “No justice, no peace”.

A spokeswoman for the US attorney’s office said prosecutors haven’t decided whether to try Swartz again on the voluntary manslaughter charge.

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“We fully respect the jury’s decision, and we thank every member of the jury for the time and attention given to this trial,” Elizabeth A Strange, first assistant US attorney for the District of Arizona, said in a statement.

Sean Chapman, Swartz’s lawyer, said his client was relieved. “He has had to live with the burden of this case hanging over his head for years. He is glad that it is finally over,” Chapman said in an email to the Associated Press.

Shot 10 times in back and head

During the trial, prosecutors said Swartz was frustrated over repeated encounters with people on the Mexico side of the border fence who throw rocks at agents to distract them from smugglers. They say he lost his cool and fatally shot Elena Rodriguez. Swartz fired about 16 rounds, and the teen was hit at least 10 times in the back and head.

Swartz had then said he was following his training and defending himself and other law enforcement officers from rocks, which he said could be deadly.

Prosecutors acknowledge that Elena Rodriguez was throwing rocks at agents while two smugglers made their way back to Mexico, but they said that wasn’t justification for taking his life. Members of Elena Rodriguez’s family maintain he wasn’t throwing rocks and was killed while walking home.

Speaking to Al Jazeera earlier this year, Elena Rodriguez’s grandmother Taide questioned how officials would have reacted had it happened the other way around. “What if a Mexican official had fired into the US, killing a US citizen. This would have been an international crisis,” she said.

On Thursday, Taide expressed disappointment in the verdict, saying that the possibility for getting justice now seems small.

“We will keep on waiting and like before we will hope to see a miracle happen,” she told Al Jazeera by phone after the Wednesday’s verdict. “But that is what it will be: a miracle. That’s what we always hoped for.”

Swartz still faces a civil rights lawsuit from the American Civil Liberties Union on behalf of the teen’s mother.

A US pro-migration activist holds a candle and a picture of slain Mexican youth Jose Antonio Elena Rodriguez through the border fence between Mexico and the US in Nogales [File: Alonso Castillo/Reuters]

Wednesday’s verdict comes as President Donald Trump has deployed troops to the border to support US authorities in response to thousands of Central American migrants and refugees who have made their way to the US border as part of a caravan, dubbed the Central American exodus. The troops have been given authority to protect Border Patrol agents and other personnel, even though there have been no instances of violence against US authorities.

Trump on Thursday, renewed his threats to close the border if things get to a “level where we are going to lose control”, adding that he has given troops the “ok” to use lethal force against migrants and refugees “if they have to”.

Additional reporting by Jurriaan van Eerten.