MEXICO CITY — Miguel Angel Trevino Morales, the notoriously brutal leader of the feared Zetas drug cartel, has been captured in the first major blow against an organized crime leader by a Mexican administration struggling to drive down persistently high levels of violence, a U.S. federal official confirmed.

Trevino Morales, known as “Z-40,” was captured by Mexican Marines in Nuevo Laredo, the Mexican media reported. The U.S. official who confirmed the media reports was not authorized to speak to the press and asked not to be identified.

Trevino’s capture removes the leader of a corps of special forces defectors who splintered off into their own cartel and spread across Mexico, expanding from drug dealing into extortion and human trafficking.

Along the way, the Zetas authored some of the worst atrocities of Mexico’s drug war, slaughtering dozens, leaving their bodies on display and gaining a reputation as perhaps the most terrifying of the country’s numerous ruthless cartels.

The capture of Trevino Morales is a public-relations victory for President Enrique Pena Nieto, who came into office promising to drive down levels of homicide, extortion and kidnapping but has struggled to make a credible dent in crime figures.

At the same time, Pena Nieto’s pledge to focus on citizen safety over other crimes sparked worries among U.S. authorities that he would ease back on a bi-national strategy aimed at decapitating drug cartels. The arrest of Trevino, a man widely blamed for both massive northbound drug trafficking and the deaths of untold scores of Mexicans and Central American migrants, will almost certainly earn praise from Pena Nieto’s U.S. and Mexican critics alike.

Trevino Morales’ rise from the streets of Nuevo Laredo to the top of Mexico’s drug-trafficking world was fueled by a brutality that stunned a population inured to violence.

He began his career as a teenage gofer for the Los Tejas gang, which controlled most crime in his hometown across the border from Laredo, Texas. He soon graduated from washing cars and running errands to running drugs across the border, and was recruited into the Matamoros-based Gulf cartel, which absorbed Los Tejas when it took over drug dealing in the valuable border territory.

Trevino Morales joined the Zetas, a group of Mexican special forces deserters who defected to work as hit men and bodyguards for the Gulf cartel in the late 1990s.

Stories about the brutality of “El Cuarenta,” or “40” as Trevino Morales became known, quickly become well-known among his men, his rivals and Nuevo Laredo citizens terrified of incurring his anger. “If you get called to a meeting with him, you’re not going to come out of that meeting,” said a U.S. law-enforcement official in Mexico City, who spoke on condition of anonymity because of the sensitivity of the topic.

One technique favored by Trevino Morales was the “guiso,” or stew, in which enemies would be placed in 55-gallon drums and burned alive.

Around 2005, Trevino Morales was promoted to boss of the Nuevo Laredo territory, or “plaza” and given responsibility for fighting off the Sinaloa cartel’s attempt to seize control of its drug-smuggling routes. He orchestrated a series of killings on the U.S. side of the border, several by a group of young U.S. citizens who gunned down their victims on the streets of the American city. American officials believe the hit men also carried out an unknown number of killings on the Mexican side of the border, the U.S. official said.