BOGOTA, Colombia (AP) -- Authorities were pressuring a top paramilitary commander Friday to surrender and face allegations he ordered hit men to kill his warlord brother, a founder of the right-wing militia and one of the most famous figures in Colombia's four-decade civil war.

Vicente Castano is accused of masterminding the murder of his younger brother, Carlos, the co-founder of the United Self-Defense Forces of Colombia, or AUC, who disappeared in 2004.

Unconfirmed reports suggested that fellow AUC members executed Carlos, believing he was going to negotiate with U.S. authorities for a more lenient sentence by informing on other commanders involved in drug trafficking and revealing their smuggling routes.

On Thursday, Vicente's bodyguard and driver Jesus Ignacio Roldan, who authorities believe pulled the trigger on behalf of his boss, was surrendered to authorities.

Five other people have been arrested in the case, including two witnesses to the purported fratricide, chief federal prosecutor Mario Iguaran said this week.

But so far, Vicente has defied orders to turn himself in and join more than a dozen other paramilitary commanders at a detention center in the western province of Antioquia.

Interior Minister Carlos Holguin issued an ultimatum to Vicente, saying if he didn't turn himself in soon, he'd lose generous benefits under a peace accord he helped broker with the government on behalf of the AUC, including reduced jail sentences and protection from extradition to the United States.

The elder Castano, known as the "Professor," has helped negotiate a peace accord with the government that has led to the demobilization of more than 30,000 fighters. If found responsible for ordering his brother's killing, he would face a maximum of eight years in prison under the terms of the peace accord, authorities say.

The alleged attack on Carlos Castano occurred in April 2004 on a farm 300 miles northwest of the Colombian capital of Bogota. Four of his bodyguards also were reportedly killed.

Carlos' disappearance caused widespread speculation across Colombia. Some, including Vicente, suggested he had reached a deal with the United States and moved there, while others said he was hiding in Israel, which he often praised for its security policies.

Carlos was a central figure of the Colombian underworld for two decades, working with the late drug lord Pablo Escobar — before joining the so-called Pepes, a shadowy group that hunted Escobar and killed many of the kingpin's associates.

He united 18 different blocs of paramilitaries under the AUC banner and led the group through its bloody national offensive against leftist rebels in the 1990s. During that period, the AUC also killed prominent leftist politicians, celebrities and presidential candidates, as well as the rebels' civilian supporters and peasants caught in the middle.

Carlos released a book called "My Confession" that was widely read in Colombia. The book was even reviewed in the New York Review of Books.

In his final years with the AUC, he was increasingly elbowed aside by a new wing of paramilitary leaders more closely tied to drug trafficking.

The spotlight now turns on the secretive elder brother, whose face most Colombians saw for the first time last year when he granted an interview.

Although Vicente has been fingered as a major drug trafficker by the U.S. government, Colombia had never issued an arrest warrant for him.