Bogota - Colombia's most feared death squad leader, Carlos Castano, is believed to have died when Marxist rebels overran his mountain stronghold in the north of the country, sources on both sides said yesterday. In a call to local media, Revolutionary Armed Forces of Colombia (FARC) guerrillas said they had killed their archenemy Castano, who had led a 10-year "dirty war" against the rebels and suspected civilian sympathisers, in fighting that began on Sunday.