That momentum of his career was cut short, however, by the traumatic time in prison tafter taking part in the demonstrations of May 1967 in Valencia against Francoist regimen. After standing up for a friend who was being brutally beat, a plainclothes agent arrested Castejón. He received several beatings that night and short after that was sentenced to six years in prison. Until mid 1969 remains in prisons of Valencia and Teruel. That year became part of the Grup d'Elx in its second stage, participating in their exhibitions until 1971. On these facts, re-enters the prison in the Canary Islands during seven months of 1971. While in prison he draw around two thousand drawings with wax or pencil, and define another specific stage of production.