He became a prominent landowner in Córdoba Department and in 1995 he joined the "Autodefensas Campesinas de Córdoba y Urabá" paramilitary group, citing being tired of guerrilla extortion and abuses that the Colombian authorities failed to prosecute. The attacks by the guerrillas to the estate owners in the region brought as a consequence the formation of illegally armed self-defense groups to confront them. This new movement had the sympathy of some sectors of the Colombian Government such as politicians and some security forces, including then-current and former members of the Colombian National Army. The group was originally under the command of Carlos Castaño, with Mancuso as his main Lieutenant.