WASHINGTON/MEXICO CITY (Reuters) - The arrest of the son of Joaquin "Shorty" Guzman's deputy at the U.S.-Mexico border was an important break in the operation that led to the drug lord's capture, a senior U.S. law enforcement official said on Sunday.
Following the arrest of Serafin Zambada-Ortiz, subsequent wiretaps and phone records of others provided investigators with leads that played a role in the arrest of Guzman, two people familiar with the matter said.
Guzman, who long ran the feared Sinaloa Cartel and was Mexico's most wanted criminal, was caught on Saturday in his native northwestern state of Sinaloa with help from U.S. agents.
It was a major victory for the Mexican government in its fight against powerful drug gangs and for the cause of cooperation between Mexican and U.S. security forces.
One of several key elements in Guzman's downfall started with the arrest of Zambada-Ortiz, the son of Guzman's deputy, Ismael "El Mayo" Zambada, who could now be in line to take over from his boss.
The break came when Zambada-Ortiz was arrested in November trying to cross the border from Mexico into the United States, where he faced sealed drug charges.
"There's not one event in this investigation that was a tipping point," the official said. "This was one of several important turning points. But it was critical."
U.S. agents seized Zambada-Ortiz's phone, but his lawyer, Michael McDonnell of La Habra, California, said no data from his client's phone or other electronics led U.S. authorities to Guzman.
Another defence attorney, Saji Vettiyil, said "There is absolutely nothing on my client's phone that would lead them to Guzman and my client has not cooperated with the authorities in any way."
U.S. prosecutors said on Sunday they plan to seek the extradition of Guzman to face trial in the United States.
Robert Nardoza, a spokesman for the U.S. Attorney's office in Brooklyn, New York, said his office would request Guzman's extradition to face a variety of charges.
A spokesman for the Mexican attorney general's office declined to comment on the extradition request. President Enrique Pena Nieto's office also declined to comment.
Sensitivities over the issue could mean Guzman is more likely to face justice first in Mexico, where he still has an outstanding term to finish. He broke out of prison, reportedly in a laundry cart, in 2001.
The United States had a $5 million bounty on Guzman's head. His cartel has smuggled billions of dollars' worth of cocaine, marijuana and methamphetamine into the United States, and fought vicious turf wars with other gangs across Mexico.
Zambada-Ortiz, who is a U.S. citizen, entered the United States at Nogales, Arizona, to take care of a visa matter for his wife, the U.S. official said.
He apparently did not know that he was facing sealed cocaine and methamphetamine charges in San Diego when he crossed the border.
Immigration and Customs Enforcement (ICE) agents arrested him and seized his phone. The Drug Enforcement Administration (DEA) often compares numbers in seized phones with a database of more than 1 billion records, which includes information collected by subpoena, search warrants and arrests during other drug investigations.
The DEA and ICE often use wiretaps and metadata from those wiretaps - numbers dialled, for instance - to locate members of large drug organizations. It could not be confirmed if this technique was used in this case, but court records show that in a related drug case U.S. authorities wiretapped between 30 and 100 telephones.
The DEA also receives information on Mexican cartel telephone and email data from the U.S. National Security Agency, but U.S. officials declined to say whether the NSA played a role in the case.
"We handled this case like we handled many: using technology to work up the chain, person by person, to the top," the U.S. official said.
Last week, that trail led them to some of Guzman's senior henchmen but the drug boss himself narrowly escaped, using a network of tunnels and sewers to give his pursuers the slip.
Guzman, 56, was eventually captured on Saturday in a pre-dawn raid on a seaside condominium in the northwestern tourist resort and fishing and shrimp-processing centre of Mazatlan, 135 miles (220 km) from Guzman's suspected base in Culiacan.
"This is the biggest success in the drug war in 20 years, and shows that contrary to what you hear in the press, behind the scenes the U.S. and Mexico have been working well together," said another senior U.S. official.
In addition to facing U.S. criminal charges in Chicago and New York, Guzman was indicted in 2007 in Miami for cocaine smuggling with additional charges added last month.
Guzman also was charged in 2012 in Texas with importing cocaine and marijuana, money laundering, firearms violations and running a criminal enterprise that included murder.
More than 80,000 people have been killed in Mexico's drugs war over the last seven years with much of the violence in western and northern regions that have long been smuggling routes.
Many of the victims are tortured and beheaded and their bodies dumped in public places or in mass graves. The violence has ravaged border cities and even beach resorts such as Acapulco.
(Corrects headline, first paragraph and other references to reflect that the arrest of Zambada-Ortiz and the subsequent wiretaps and phone records of others, not the seizure of the man's phone, played a role in the capture of Guzman)
(Additional reporting by Simon Gardner in Mexico City and Mark Hosenball in Washington; Editing by Kieran Murray, Grant McCool and Mohammad Zargham)