By JUAN FORERO
 
BOGOTÁ, Colombia, April 24 — The recent disappearance of Carlos Castaño, the longtime chief of Colombia's right-wing paramilitary force, has focused attention on a paramilitary leader closely linked to the cocaine trade who is seen as the one with the most to gain from Mr. Castaño's disappearance.

The man, Diego Fernando Murillo, 42, was described by a major paramilitary commander, a paramilitary aide, and political analysts as the main beneficiary of a plan to assassinate Mr. Castaño, who was the driving force behind the paramilitary movement.

Mr. Castaño's disappearance has thrown American-backed peace talks with the government into turmoil, and many people who have been following the talks are pointing fingers at Mr. Murillo, who is better known as Don Berna or Adolfo Paz.

Rodrigo Franco, a renegade commander who broke with other commanders over what he says were their ties to drug trafficking, said that, "With this, Don Berna has finished consolidating his power."

Though no one knows what happened to Mr. Castaño in the attack on him on April 16 — he was either killed or he escaped — the disappearance underscored that a loose coalition of paramilitary groups involved in peace talks with President Álvaro Uribe's government is now more heavily influenced than ever by drug trafficking.

"Narco-trafficking has been imposed," he said, "as well as its tactics and strategies."

Mr. Castaño's absence also means that Mr. Murillo is now the most influential of several paramilitary commanders in the 15,000-member federation, the United Self-Defense Forces of Colombia.

"Today, he is the most powerful man in the paramilitaries," said Wilson Borja, a congressman who was severely wounded in an assassination attempt orchestrated by paramilitaries. "They say he is the military inspector, but he runs it all."

An American official said recently, "He is a key player because the paramilitary folks are afraid of him, and for good reason."

"He is an enforcer," the official, who helps guide American policy in Colombia, added. "He is a butcher."

Though the paramilitaries are well known for their brutality, their primary purpose is a political one, eroding support for Marxist rebels by killing peasants and supporters.

The federation of paramilitary groups has always had ties to traffickers, with the first groups founded by cocaine lords. But Mr. Murillo, a rotund man with a bushy mustache who describes himself as "enigmatic," is considered the commander most heavily rooted in Colombia's cocaine underworld. He has been linked to assassinations in Medellín, the Colombian drug capital, and had close ties to the country's notorious cocaine kingpin, Pablo Escobar.

Government investigators determined that Mr. Murillo later turned on Mr. Escobar and is now the de facto leader of a drug-trafficking wing of the paramilitaries. That wing includes Vicente Castaño, who is Carlos Castaño's brother, and Salvatore Mancuso, an educated cattleman whose children vacationed in Boston at the same time the United States was seeking his extradition on trafficking charges.

Those men, political analysts and Western diplomats say, are focused on maintaining their ill-gotten gains, vast tracts of land and offshore bank accounts. They have given no sign that they are dismantling their trafficking network.

Instead, they have been using the peace talks as a vehicle to legalize their status and avoid extradition.