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.
The final say over extradition and which U.S. court would try Guzman first is up to Attorney General Eric Holder, who has not made a decision.
One federal official told ABC News that there's "an expectation" that if Guzman is extradited, he would be sent to New York to face trial in Brooklyn federal court.
"We are fully expecting to prosecute him in Brooklyn," one official told ABC News.
As in the case of high-value detainees in terror cases, New York is often viewed as the prime venue because the Justice Department has the infrastructure, security and media accommodations there to handle trials of international significance with dangerous defendants.
Other U.S. attorneys, including those in Chicago, San Antonio and Washington, D.C., would also like the chance to try Guzman.
Guzman, whose nickname is slang for "shorty," is the alleged CEO of the Sinaloa cartel, which is estimated to move 25 percent of all illegal drugs entering the U.S. through Mexico. He is facing drug trafficking and multiple other charges and is wanted in at least six U.S. districts and Mexico.
The cartel is also heavily involved in crime and carnage arising from the bloody drug war that has swept Mexico and the U.S. over several years.
Last February, the Chicago Crime Commission branded Guzman the first "Public Enemy No. 1" since Al Capone, leading to him being dubbed as "El Chapone," in the shadow of Chicago's other great criminal.
The DEA has said in the past that as much as 90 percent of the marijuana, cocaine, heroin and other illegal drugs sold on the streets of Chicago are supplied by the Sinaloa cartel. Guzman is also charged with drug trafficking, murder, kidnapping and other crimes in New York.
The alleged drug kingpin has also long been ranked among the richest men in the world by Forbes and drug enforcement experts had conservatively estimated the cartel's revenues at over $3 billion annually.
Before his infamous 2001 Mexican prison escape, Guzman had been serving a 20-year sentence for bribery and criminal association.
ABC News' Pierre Thomas and Josh Margolin contributed to this report.