Devil in the Brain (1972)

Oscar is trying to re-establish an affair with Sandra, a disturbed young woman. Having found her husband Fabrizio shot dead and her young son Ricky standing beside him with a gun, Sandra suffered a complete breakdown and now lives in isolation with her protective mother. The latter saved the young boy from recrimination by placing the gun in his father's hand, making it seem like he committed suicide. However, things are not what they seem...