And how much would it matter if he did? Experts suspected he had delegated much of the day-to-day work, and drugs have been moving north from this fertile region since World War II, when the American government needed opium for its wounded soldiers. With demand for heroin surging yet again, no one doubts that the trade — “the life,” as some here call it — will go on.

But with momentum building in Culiacán, American officials said that the Mexican marines began to believe they might actually get the target that had slipped their grasp so many times before.

A small team of American agents with the D.E.A. and the United States Marshals Service were embedded with the Mexican marines, American and Mexican officials said, and in their ranks, too, confidence was rising, and mixing with impatience. As days dragged to weeks, there was a sense that Mexican officials wanted to wrap things up — especially after a raid led to what appeared to be a near miss.

Working on information from some of Mr. Guzmán’s bodyguards, Mexican marines and American agents raided the home of his ex-wife on Thursday. After struggling to batter down the steel-reinforced door, according to the Mexican authorities, they were too late: instead of finding their prey, they discovered a secret door beneath a bathtub that led to a network of tunnels and sewer canals that connected to six other houses.

The search continued, but the earlier arrests and intelligence were pointing south, to Mazatlán — one of Mexico’s first resorts.

Mr. Guzmán was not known to spend much time here; local businessmen with a lifetime of knowledge about Sinaloa’s connections to the community said there were no known Chapo sightings, or serious rumors, over his many years in power.

The building he chose, called the Miramar, was built about a decade ago, they said, and was filled with a mix of vacationers — Mexicans and American and Canadian retirees — who came and went through the year. Before dawn on Saturday morning, it seemed to be just another place to enjoy the view. But about 12 hours earlier, an intercepted phone call to Mr. Guzmán’s cellphone had already triggered the command to move. In the dark of night, neighbors heard knocks on the doors, according to interviews via apartment intercom. American officials said the teams did not know which apartment he was in. Then came a crash.