 It was Moisés Guevara who brought him into Che Guevara's Ñancahuazú guerrilla group in March 1967.Selected to be a member of the "center" unit which was led by Che Guevara himself, Willy came to be known as a disciplined and courageous combatant.Despite this, and perhaps as a result of his extremely reserved nature, Guevara developed suspicions about him and in his monthly summary for September 1967 wrote in his campaign diary that "The morale of the rest of the group has remained quite good, and I only have doubts about Willy, that he may take advantage of some havoc to try to escape by himself ... " His suspicions would soon prove to have been unfounded.