The young men were returning home from a nightclub in Nuevo Laredo, which is regularly the scene of violence attributed to drug traffickers, when they were chased by troops.

The military said afterwards that soldiers on patrol had heard gunshots and saw a pick-up truck without lights or license plates whose driver tried to escape.

The Nuevo Laredo Human Rights Committee said that a military captain revealed during the trial that the four soldiers had opened fired without authorization from a superior.

The United Nations human rights office welcomed the sentence, saying "accountability for actions of this gravity is essential to guarantee justice for the victims and prevent their recurrence."

According to New York-based advocacy group Human Rights Watch, Mexican police, prosecutors and soldiers commit "widespread abuses" including torture, arbitrary detention and extrajudicial killings.

The army killed 5,488 civilians from 2007 through July 2023 and the deaths are rarely independently investigated, it said in its World Report 2024, citing government data.