The key to capturing one of the world's most wanted men may have been the thing he held dearest: his family.
Joaquin "El Chapo" Guzman had been on the lam for more than a decade, eluding authorities who say he is at least partially responsible for "the death and destruction of millions of lives across the globe," as Attorney General Eric Holder put it.
But last month, U.S. law enforcement agencies -- particularly the Drug Enforcement Administration, Immigration and Customs Enforcement and the U.S. Marshals -- thought they might finally be on his trail, a law enforcement source told ABC News.
The operation to catch Guzman was first sparked by an ICE Homeland Security Investigations case based in Arizona, where federal agents were targeting Sinaloa associates inside the United States. With help from DEA and others, that effort blossomed into a much larger probe, ultimately ensnaring Guzman.
U.S. efforts to disrupt Guzman's deadly Sinaloa cartel had focused on the organization's distribution network and structure, including how orders and instructions flowed through the cartel. Authorities came to realize that many of the people carrying out orders were Guzman's own family members, the source said.
What's more, authorities noticed that some of those family members would seek various approvals from a specific cartel member whom authorities had yet to identify. And, authorities recently learned, the unidentified cartel member would also exchange particularly personal messages with Guzman's family members -- messages so personal that the "unidentified cartel member" could only be Guzman himself.
Finding Guzman, though, was no easy task.
In recent weeks, as Mexican law enforcement arrested more associates of Guzman and gathered more intelligence with help from the U.S. government, authorities were able to identify locations Guzman frequented and patterns of his personality, the law enforcement source said.
Nearly a week ago, authorities raided a hideout in Culiacan, Mexico, but Guzman narrowly escaped through a tunnel. Some of his associates were arrested, providing even more potential sources of intelligence for the manhunt.
On Friday, authorities tracked Guzman to a hotel room in Mazatlan, Mexico. They spent that night trying to confirm -- once and for all -- that Guzman was inside, as Mexican authorities drafted a plan to take him into custody.
No shots were reportedly fired as Mexican marines burst into Guzman's room at the Miramar Hotel 6:40 a.m. Saturday.
Video released today by Mexican authorities showed the messy room in which Guzman was finally caught. When he was snatched, breakfast was still on the stove, an indication of his abrupt departure. Not a shot was fired during his arrest.
The question remains where Guzman will be prosecuted.
While he was taken into custody by Mexican authorities, he has been indicted by U.S. authorities in Brooklyn, N.Y., and the U.S. attorney there is planning seek his extradition to try him there, according to Robert Nardoza, the spokesman for U.S. Attorney Loretta Lynch.
But Guzman also faces charges in Mexico and elsewhere in the United States, and because of that it is not clear what will happen to him and in what order.