Trevino Morales is expected to be succeeded by his younger brother, Omar, a former low-ranking turf boss who's seen as a far weaker figure.
Miguel Angel Trevino Morales 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.
Trevino Morales' brother, sister and mother lived in Dallas but he had many relatives around Nuevo Laredo and, while moving frequently to avoid authorities, was believed to often return to his hometown, the U.S. official said.
Trevino Morales joined the Zetas, who worked as hit men and bodyguards for the Gulf cartel, in the late 1990s.
Stories about his brutality quickly became well-known among his men, his rivals and Nuevo Laredo citizens terrified of incurring his anger.
One technique he favored was the "guiso," or stew, in which enemies would be placed in 55-gallon (208-liter) drums and burned alive, said a U.S. law-enforcement official in Mexico City, who spoke on condition of anonymity because of the sensitivity of the topic. Others who crossed the Zeta commander would be beaten with wooden planks, the official said.
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, according to U.S. and Mexican officials. 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 Laredo.
In 2006, the Gulf Cartel and the Zetas defeated the Sinaloa cartel in Nuevo Laredo, a victory that emboldened them as they began spreading south to towns and cities that had never before seen extensive organized crime. They set up criminal networks to control transit routes for drugs, migrants, extortion, kidnapping, contraband of pirated DVDs and CDs, and countless other criminal activities.
According to the U.S. official, Trevino Morales was in charge of Nuevo Leon, Piedras Negras and other areas until March 2007, when he was sent to the city of Veracruz following the death of a leading Zeta in a gunbattle there.
That same year, Trevino Morales and Lazcano began pushing for independence from the Gulf Cartel after cartel head Osielo Cardenas Guillen's extradition to the U.S.
By 2008, the Zetas operated in 28 major Mexican cities, according to an analysis by Grupo Savant, a Washington-based security think tank.
In February 2008, Lazcano sent Trevino Morales to Guatemala, where he was responsible for eliminating local competitors and establish the Zetas' control of smuggling routes. Trevino Morales was then named by Lazcano as national commander of the Zetas across Mexico despite his lack of military background, earning him the resentment of some of the original ex-military members of the Zetas, the official said.
The promotion involved Trevino Morales in virtually every decision by the Zetas, the official said.
Trevino Morales was indicted on drug trafficking and weapons charges in New York in 2009 and Washington in 2010, and the U.S. government issued a $5 million reward for information leading to his arrest.
According to the indictments, Trevino Morales coordinated the shipment of hundreds of pounds of cocaine and marijuana each week from Mexico into the U.S., much of which had passed through Guatemala.