During the internal conflict that began in the 1980s, Castillo worked in his youth as a patrolman of the Ronda Campesina to defend against Shining Path. A former student of Castillo, Nilver Herrera, followed him into the Ronda Campesina, saying that Castillo "was always trying to help people, ... If we had to build a road, he was there, if we had to do some task or errand, he was there, and if we had to help a sick person who didn’t have money, he was there." These groups held certain leftist beliefs, though they combatted left-wing terrorism in rural areas not under the scope of the Peruvian government.