There are many ways to climb through the ranks of a Mexican drug cartel: family connections, business acumen, and the ability—some might say willingness—to follow orders, no matter the order. Most take time, patience, perhaps even a little bit of subtlety.

And then there is the quick way: repeated acts of mind-numbing, outrageous violence. For Miguel Angel Trevino Morales, known as Z-40, the leader of arguably the most feared and certainly the most violent cartel operating in Mexico, the path of violence wasn’t simply a means to the top—it was a way of life.

A unit of Mexican Marines arrested Morales without incident early Monday morning, putting an end (at least for now) to the reign of one of the most bloodthirsty murderers in modern Mexican history. “He was a crazy, nasty, violent guy,” says Sylvia Longmire, consultant and author of a recent book, Cartel: The Coming Invasion of Mexico’s Drug Wars. “If there was a choice, he always killed in the ugliest way possible,” Longmire said. She cites Morales’s uniquely grotesque passion for boiling down the bodies of his enemies into a pozole, a kind of stew, resulting after bodies were dumped in vats of acid from which only sets of stained teeth remained.

Dismemberment, beheadings, public executions—many of the hallmarks of the last several years of Mexico’s bloody struggle against the cartels bore the signature marks of Morales’s taste for brutality. The bloodier, the better. “Cutting people up and putting them into a pozole, there was probably a little bit of both,” says Longmire. “Dead and alive.” But it wasn’t all blood and gore. With the help of a brother, Morales also developed a sophisticated money-laundering scheme in Texas and Oklahoma, buying and selling quarter horses for millions of dollars in drug money.

Morales’s arrest was seen as a major victory for Mexican president Enrique Peña Nieto, who won office partly on promises of taking a different course in tackling the drug trade begun by his predecessor, Felipe Calderón. The arrest was allegedly the result of at least eight months of painstaking intelligence work and, many experts agree, probably the benefitted from at least one informer close enough to Morales to know the details of his travel schedule.

Many had criticized Calderón’s “kingpin” strategy for leading to more —and more horrifyingly brutal—violence for ordinary Mexicans caught up in the torrent of the drug war’s out-of-control spiral. With the arrest of Morales, some observers say Nieto has regained the upper hand. “The arrest of Z-40 is obviously a big success for the new administration, which some U.S. officials were reportedly worried wouldn't stay the current course against the drug cartels that Calderón started,” says Malcolm Beith, author of The Last Narco, a 2011 book about the hunt for El Chapo Guzmán, head of the Sinaloa cartel and Morales’s former boss. “This arrest shows the Peña Nieto administration is at least intent on continuing the kingpin strategy.”

Morales began as a “Mickey Mouse smuggler,” says Rusty Fleming, an author and documentary filmmaker who spent years cultivating sources within Los Zetas that ultimately led to a documentary about the cartels. Fleming says Morales rose quickly by the force of his violence. By “killing his way to the top,” says Fleming, Morales helped transform the Zetas from a wing of armed enforcers working for El Chapo and the Sinaloa cartel into what would eventually become a powerful cartel in its own right and the most significant rival to El Chapo’s domination. When Morale’s predecessor, Heriberto “the Executioner” Lazcano died in October 2012, Morales took over and continued the group’s spread, eventually putting his own people in charge of the many “plazas” and “gates”—terms for the bridges and zones where the bulk of the drug trafficking occurs—across Nuevo Laredo and Tamaulipas, along the U.S. border.

One of Morales’s signature moves was to identify young recruits, sometimes called Zetistas, who showed promise in cultivating the kind of brutality he relished. Fleming, Longmire, and others say Morales recruited boys as young as 12 and 13 into the organization as smugglers, scouts, and, in several cases, assassins. “He didn’t care how old you were, it was about what you were willing to do,” says Fleming. “He didn’t mind giving a 15-year-old a hundred-thousand-dollar Mercedes if he had earned it.”

Morales’s absence is likely to spawn a power vacuum as the lower-ranking members grapple for the spoils. One contender is Omar Alejandro, Morales’s brother and the most high-profile member of the remaining leaders. “It can be seamless, quiet, but there has always been a question of can he fill Z-40’s shoes? Does he have the confidence?” asks Longmire. “On other hand, if they perceive weakness, then you start to have internal fights for power—that gets ugly.” Longmire says the next couple of weeks will be key, and that unfortunately “it will be the body count that determines who stays in power.”

Meanwhile, there are signs that the reach of Los Zetas under Morales’s brutal reign has extended farther south, and with worrying consequences. Richard Valdemar, a former L.A County sheriff, says there are indications the Zetas have been teaming up with bands of former Guatemalan Special Forces, called Kabiles, opening up the Mexican cartel to new pathways for cocaine through Central America. “Groups of these Guatemalan Special Forces have defected and are aligned with the Zeta cartel, and that's very dangerous because they have the same kind of background,” says Valdemar, “As drugs come through the southern part of Central America and need security, they have formed alliances, and now they are forming a paramilitary link through the continent.”

As it is, Mexican cartels have become increasingly powerful north of the border, operating in over 1,200 U.S cities, according to the Justice Department and independent observers. The move farther south fits in with what many say is a larger, continental ambition. It’s a legacy of which Morales no doubt will be proud, but which most everybody else will fear could be the next front in Mexico’s bloodiest war.