My Dear Killer (1972)

Following the mysterious decapitation (via mechanical digger) of an insurance investigator, Police Inspector Peretti is put onto the case. Slowly more people are found dead--a man supposedly commits suicide, a woman is strangled, another attacked in her flat--but all the clues lead to an unsolved case of kidnapping and murder. Can Peretti find the murderer if his major clue is a little girl's drawing?