'Savage Three' aka 'Fango Bollente' (1975) – Vittorio Solerno.

Maestro Vittorio Solerno's raven dark poliziottesco 'Savage Three' exposes the increasingly bestial proclivities of three workmates, headed by handsome hedonistic brute Ovidio (Joe Dallesandro). Spending the days working anonymously for a modern-looking data collection firm but spending their nights perpetrating myriad barbarous acts of arbitrary violence. The Savage Three are not political upstarts, their spontaneous campaign of cruelty, blithely orchestrated to assuage the monotony of a dour, stultifying regimented office life. These ruthless crimes drawing the attention of laconic commissario Santaga (Enrico Maria Salerno), an idiosyncratic sleuth whose hunch that the grisly killing spree is the work of amateur thrill killers marking him out to be an eccentric maverick! The dogged Santega's unerring gut instinct leads him ever closer to the inscrutable Ovidio, his psychotic debaucheries, exploding in a final, fatal act of stomach-churning savagery from which there is no return. Solerno's disturbingly brutal narrative, while remarkably explicit, has a profound intelligence, giving Savage Three an emotional gravitas that feels uncomfortably relevant even today.