Heriberto Lazcano, the leader of the Zetas drug cartel in Mexico, has apparently been killed in a shootout with marines, according to the country's navy.
The navy said there was strong evidence after the firefight in the northern border state of Coahuila that Lazcano, known as El Lazca, was one of two men who died. But it added that further forensics tests would have to be carried out to confirm the identification.
"Information was obtained after the first forensics tests were carried out that yielded indications that suggest that one of the bodies is Heriberto Lazcano," the navy's statement said.
"The navy department is co-ordinating efforts with Coahuila state and will be awaiting the conclusions of the forensics examination in the case."
The death of Lazcano would be a major victory for Mexican law enforcement. The Zetas cartel that he helped found with other deserters from an elite army unit has gone on to carry out some of Mexico's bloodiest massacres, biggest jail breaks and fiercest attacks on authorities.
Lazcano, who is also known as El Verdugo (the executioner) for his brutality, is suspected in hundreds of killings, including the death in June 2004 of Francisco Ortiz Franco, editor of a crusading weekly newspaper in Tijuana that often reported on drug trafficking. Ortiz Franco was gunned down in front of his two young children as he left a clinic.
The US has offered a $5m reward and Mexico an additional $2.3m for information leading to Lazcano's arrest.
Under Lazcano's leadership the Zetas recruited more hitmen, many of them former Mexican soldiers, and hired "kaibiles" – Guatemalan soldiers trained in counter-insurgency, transforming what had been a small group of assassins into a ruthless gang of enforcers for the Gulf cartel. The Zetas were also in charge of protecting the Gulf cartel's drug shipments.
The Zetas finally split from their former bosses in 2010 and have since been fighting a vicious battle for control of the drug business in north-eastern Mexico, traditional home base of the Gulf cartel. The result has been a surge of drug-related killings.
Lazcano "is credited with strengthening the organisation ... he created a new structure of regional cells that specialise in specific crimes", Mexican federal prosecutors say in their profile of Lazcano.
The Zetas earned their notoriety for brutality by becoming the first to publicly display their beheaded rivals, most infamously two police officers in April 2006 in the resort city of Acapulco. The severed heads were found on spikes outside a government building with a message signed "Z'' that said: "So that you learn to respect."