 The film contains some very violent murders, some shown from the point of view of the knife-wielding, black-gloved killer, as he stabs a woman in her bed, bashes in the head of a prostitute, strangles a female artist with a telephone cord, drowns a mental patient in her bathtub, and even uses a power drill on one unfortunate victim.Mario must catch the real killer in order to prove his own innocence.Towards the 1970s, Umberto Lenzi began focusing his attention on "poliziotteschi" films and his contributions to making "gialli" began to deteriorate.