YET, his legal problems continue to pile up. Mr. Leyzaola is now scheduled to appear before a judge to address allegations tied to his time in Tijuana. A recent report from the Human Rights Commission there argued that he and several subordinates tortured four police officers suspected of corruption in 2010. An earlier report linked him to the deaths of five people accused of killing police officers in 2009.

He has denied those allegations, insisting that the claims are an effort to smear him. He also denies having anything to do with the case of four young men here in Juárez who were found dead in a tunnel a few weeks after witnesses saw them detained by the police on March 26.

“I had only 10 days on the job when this started,” he said. “What did we do in this case? I was the one who insisted that those responsible are punished.”

Chief Leyzaola (who failed to mention that only a few of the 15 officers accused in that case have been arrested) says he is mainly struggling with a young and ill-equipped police force. He has already fired about 200 officers, and he said more were likely to be purged. In addition to the challenge of recruiting — the department now has about 2,300 officers, he said, down from 3,000 a few years ago — he highlighted the challenge of training the ones he hires: “About 1,800 of the 2,300 officers have no more than two years of service.”

Many say they are inspired by their boss. Inside the police station lobby, they point proudly to a wall of newspaper clippings on arrests. Such strong morale is certainly a rarity in many Mexican police departments. But experts say that Chief Leyzaola has yet to grasp the limits of his show-how-tough-we-are approach.

“Policing is not about personalities — it’s about procedures and institutions,” said David A. Shirk, director of the Trans-Border Institute at the University of San Diego. “When Leyzaola is gone, as he inevitably will be at some point, what will be left behind? That’s the key question.”

Transparent processes for investigations and promotions matter more than tough talk or even high profile arrests, experts say. And while crime is down in both Tijuana and Juárez, it is not clear how much this has to do with Chief Leyzaola. Mr. Shirk said it likely had more to do with cartel dynamics — a truce or shift in power, with one group gaining an overwhelming edge. Some Sinaloa cartel members on trial in the United States have said they tried to work with Mexican and American authorities so they could defeat La Linea.