After the Brazilian coup d'état of 1964, Grabois became a proponent of armed struggle to overthrow the military regime. In 1966 the Communist Party of Brazil decided that urban guerrilla warfare tactics were necessary to establish a Communist regime in Brazil. In 1967 Grabois started recruiting guerilla combatants in Pará and after a series of clashes with government forces, Grabois had disappeared and later was revealed to have been killed in 1973. Contemporary reports claim he was executed by Major ; a military report places the date of his death at December 25. His death has yet to be officially recognized by the government.