“It’s so obvious to anyone with common sense that you don’t get to almost 100 percent impunity without a rottenness and corruption that’s eroded the institutions to their core,” said Mr. LeBarón, 42, who has conducted a high-profile campaign to pressure the Mexican authorities and the president’s administration to solve the case.
The family members were ambushed while driving in three sport utility vehicles in a rural area of Sonora where Mormon groups that splintered from the main United States church began settling in the early 20th century.
In the days after the attack, the authorities suggested that it could have been a case of mistaken identity, and said they were exploring the possibility that it was related to a conflict between two criminal groups fighting for control of that region and its lucrative trafficking routes for drugs, weapons and other contraband.
Because the victims had American citizenship and frequently moved between the two countries, Mexican officials agreed to give their counterparts in the United States full access to their investigative files.
When Mr. López Obrador took office in 2018, he vowed to end his predecessors’ war on drugs, an approach that had relied on the military. Instead, he promised, he would address the roots of crime by tackling poverty through social development programs and investment — a strategy he referred to as “hugs, not bullets.”
And yet, the effort has not significantly lowered the national murder tally.
Asked whether he thought there was anything to celebrate in the latest arrest in connection with his family’s case, Mr. LeBarón said, “We’ve understood who the top dogs are, and this is not one of them.”
He said the attention drawn by the case, which made international news, left him feeling an obligation to speak up for other families and to push the government to do more to reduce the nation’s violence.