During the late 1970s Cano is believed to have joined FARC, where he quickly rose through the ranks, working with the group's co-founder and chief ideologue, Jacobo Arenas. His main role was originally to serve as a sort of political commissary for the urban network of the guerrilla in Bogota, and in 1978 he was appointed chief of finances for the Central High Command. A search warrant on his apartment, where he lived with his first wife (Maria Eugenia) and son (Federico), ended in his arrest in 1981 and imprisonment in the La Modelo Penitentiary, where he founded a library. He was freed in 1983 as a result of the amnesty offered by the government of president Belisario Betancur.