The article explores the role of denunciation and collusion in driving the post Civil War judicial repression in Spain between 1939 and 1945. It argues that in recent years historians have done much valuable work to unearth the long hidden Francoist repression, but that much remains to be learnt about the complicity that lay behind the mass killing and incarceration. Accordingly, to help further our understanding of collaboration in the repression, the article offers a case study of the launching of prosecution in military tribunals. It shows that regime officials and their supporters in the community often conspired to herd their mutual political enemies through farcical summary prosecutions. It also demonstrates that in a significant number of cases the authorities followed the lead of their civilian collaborators who singled out potential victims for them. Thus it concludes that the Franco regime did not simply impose itself on society but that its supporters at the grassroots played an important role consolidating it from below.