MEXICO CITY -- The Mexican Navy confirmed on Tuesday that it had killed Heriberto Lazcano, the founder and the principal leader of the Zetas, one of the most violent criminal gangs to terrorize the country in years.
But in a striking twist, an armed group quickly stole the body, a state prosecutor said Tuesday, leaving the authorities struggling to explain how such a major blow against Mexico's criminal organizations could turn into an illustration of their persistent strength.
The navy said that it had killed Mr. Lazcano in a battle between marines and men armed with guns and grenades on Sunday afternoon in Coahuila State in northern Mexico.
His death may be one of President Felipe Calderón's biggest victories against drug and organized-crime groups, and it comes two months before the president ends his six-year term with a legacy marked by an escalation of the fight against gangs and the brutal violence they have wrought.
But even before the navy had announced the death of Mr. Lazcano, a group of heavily armed assailants, with their faces covered, showed up at the funeral home where the body was and took two corpses -- Mr. Lazcano's and that of another person killed in the navy operation. The state prosecutor in Coahuila State, Homero Ramos, said the assailants put the bodies in a hearse and forced the funeral home director to drive it away.
It would not be the first time that Mexico's powerful drug gangs have struck back after an apparent victory by the authorities. Gunmen have sprung their allies from jail, rescued them from hospitals, taken away their fallen colleagues from crime scenes and even killed family members of a special forces sailor involved in a successful raid on a top drug lord.
This instance was particularly embarrassing because authorities had to admit to losing the body even as they touted the killing as a sign that they were making major inroads in controlling the cartels.
The Zetas stand out among the country's two or three largest criminal groups for their butchery, carrying out beheadings and other mutilations to intimidate enemies and murdering those who do not follow their orders, including migrants passing through their turf, mainly in northeastern Mexico.
They have staged some of the country's most spectacular jailbreaks -- they were said to be behind one last month in which scores of inmates walked out of a state prison -- and the most brazen attacks on Mexican security forces.
Mr. Lazcano deserted more than a decade ago from an elite Mexican Army unit. Along with other former special forces operatives from Mexico and Guatemala, he founded, trained and recruited armed men to serve as enforcers for the powerful Gulf Cartel.
The Zetas split off on their own two years ago and have fought their former allies and the Sinaloa Cartel, run by the drug lord Joaquín Guzmán, known as El Chapo, or Shorty, who is wanted as badly here as Osama bin Laden once was by the United States.
Lately, security analysts have reported that the Zetas themselves are fracturing into at least two groups, and Mr. Lazcano's death, along with the recent captures of other top Zeta leaders, will probably sow even more confusion and violence among the ranks. In the scramble, Zeta leaders are believed to be turning on one another through executions and providing tips to law enforcement. Another Mexican Navy operation against the Zetas on Sunday, in Nuevo Laredo, led to the capture of a man whom the authorities said was the gang's regional leader in three border states.
Eduardo Guerrero, a security consultant who closely tracks organized crime here, said it appeared that the Mexican government, frequently acting on intelligence provided by the United States Drug Enforcement Administration, had been hitting the Zetas particularly hard and capitalizing on the divisions in the group.
He said there had been 17 major arrests of leaders of the group over the past year.
Mr. Lazcano, who is also known as the Executioner, had been wanted by American law enforcement on drug trafficking and related charges, with a $5 million reward on his head.
The marines are considered Mexico's most professional force and have made some of the most significant captures and kills in the drug war. But they are also responsible for one of the bigger fiascos in Mr. Calderón's term, when they falsely arrested a man in June who was presumed to be the son of Mr. Guzmán. Prosecutors later said it was not him.
Correction: October 9, 2012, Tuesday
This article has been revised to reflect the following correction: An earlier version of this article misstated the timing of a jailbreak in which the Zetas are believed to have been involved. It was last month, not last week.
This article originally appeared in The New York Times.