The Experts(1973)

This grim German psychological drama unveils the process by which an innocent man can be so damaged by interactions with the criminal justice system that the smallest incident can trigger a murderous fury. Matthias (Matthias Eysen) is already a misfit and has trouble meeting society's expectations. When he is picked up by the police for a minor crime, the brutal indifference with which he is treated wounds him in ways which are not healed by his being found innocent and being released.