It could be the greatest victory Mexico has seen in six years of bloody battle with drug organizations: A top Zetas drug cartel leader is believed to have been killed in a northern Mexico gunfight on Sunday.

The Zetas are the most reviled drug trafficking organization in Mexico, responsible for mass graves, brutal executions, mutilations, extortion, kidnapping, and jailbreaks across the country. And the administration of Mexican President Felipe Calderón has been putting pressure on the group in recent months.

“It is a huge deal for the government,” says Ana Maria Salazar, a former Pentagon official and security analyst in Mexico City. “When you have organizations that are this dangerous, the government has to prioritize and go against those organizations that most exercise violence against society in general. It is a good strategy in that sense.”

‘The Executioner’ killed?

The founding leader, Heriberto Lazcano, who is known both as “El Lazca” and also “El Verdugo,” or "the Executioner," is believed to have been killed in Coahuila, in northern Mexico, in a Sunday fight that broke out between gunmen and the Mexican Navy.

"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 Mexican Navy said in a statement. "The Navy department is coordinating efforts with Coahuila state, and will be awaiting the conclusions of the forensics examination in the case.”

If it is confirmed, it would be a blow to one of the most ruthless organizations in a savage drug war that has taken some 60,000 lives in six years. Mr. Lazcano is a founding member of the Zetas, who are former elite Army deserters who also recruited “kaibiles” or elite Guatemalan soldiers. The group started as the armed enforcement for the Gulf cartel, before splitting in 2010.

While all of the drug organizations display unfathomable brutality, the Zetas are considered among the most vicious, the first to publicly display beheadings as an intimidation measure and leaving a signature 'z' at crime scenes.

A double blow

This death comes as another Zetas suspect was arrested by the Navy in Nuevo Laredo, across from the Texas border. That suspect, Salvador Alfonso Martinez Escobedo, was arrested during the weekend, according to the Navy. He is accused of leading of one of the most violent moments in the drug war: the massacre of 72 migrants in Tamaulipas in 2010. He is also linked to major jailbreaks in recent years and the infamous killing of David Hartley, an American, on Falcon Lake at the US-Mexico border.

Mr. Martinez’s arrest follows sustained pressure against the Zetas in recent months. Eduardo Guerrero, a security consultant, told The New York Times that he counts 17 major arrests of leaders of the Zetas over the past year.

The end of the Zetas?

But this does not mean the end of the Zetas. Analysts have said the group has splintered: “As we have seen in other parts of the country, this could lead to fragmentation,” says Javier Oliva Posada, a drug expert at the National Autonomous University of Mexico. “It could mean an increase of violence in the short-term.”

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Mr. Oliva Posada faults the Calderón administration for not having a full-scale strategy beyond simply going after top cartel leaders. That, with a dysfunctional justice system, has meant death tolls and levels of violence are at historic highs in Mexico. Many of those arrested are either let go because there is not enough evidence against them, or in some cases, they walk out of jail during jailbreaks.

“Regardless of what happens with Lazca, whether he was killed or not, the truth of the matter is that … the [Zetas] will continue with the business of drug trafficking,” says Ms. Salazar.