Police said Thursday morning that the man arrested was in fact Gustavo Alvarez Tellez, alias "El Gordo," thought to command Bonilla's network of assassins on the Caribbean coast. He was detained on the Dutch island of Aruba, and has an extradition order pending from the U.S., police said.

Alvarez is among the 15 operatives believed to be closest to Bonilla. Originally from the department of Caldas, he began his criminal career in a paramilitary group, the Peasant Self-Defense Forces of Puerto Boyaca (Autodefensas Campesinas de Puerto Boyaca). After the group demobilized in 2006, Alvarez began working closely with the Oficina's third-in-command, Fabio Velez Correa, alias "Nito," who was killed in September 2009 for attempting to negotiate his surrender to authorities.

Last year, Alvarez was reportedly the target of a massacre in a Medellin nightclub in June, which left eight people dead. Since then, he has apparently been based in Cartagena, coordinating Bonilla's network of assassins, as well as managing drug shipments to the coast.

The original leader of the Oficina, Diego Murillo, alias "Don Berna," was extradited to the U.S. in 2008. Soon afterwards, his appointed succesor, Carlos Mario Aguilar, alias "Rogelio," turned himself in. Since then Murillo's protege, Bonilla, has faced a bloody war with a rival faction of the Oficina, led by Erick Cardenas Vargas, alias "Sebastian."

The arrest of Alvarez, one of Bonilla's confidants, may be an indication that authorities are closing in on the crime lord. Since the assasination of alias "Nito" in 2009, Bonilla has been paranoid that his associates may be clandestinely negotiating to give him up, which has helped fuel violence within the Oficina.

In April 2010, the U.S. issued an extradition order for Bonilla and offered a $5 million reward on his head, putting Bonilla under great pressure. Aside from Vargas, rival group the Rastrojos are also intent on seeing him captured or killed.