He later became a member of both Ordine Nuovo and FUAN (Fronte universitario d'azione nazionale), the university arm of the Italian Social Movement (MSI).
Concutelli was suspected of murdering two ETA volunteers who had been hiding in France, having allegedly been commissioned by Delle Chiaie to carry out the killings.
On 10 July 1976, he killed Deputy Prosecutor Vittorio Occorsio in Rome as punishment for carrying out investigations targeting neofascists, including several who were associated with Ordine Nuovo.
"[4] In February 1977 he was arrested by an anti-terrorist squad, and following a year-long trial was shown the nature of "bourgeois justice" for himself when he was sentenced to life imprisonment for Occorsio's assassination.
Initially held in Regina Coeli prison, Concutelli was later transferred to the maximum-security penitentiary in Novara, where he was responsible for the murders of several fellow inmates.