Bird With the Crystal Plumage (1970)

An American writer traveling in Rome is the only witness to an attempted murder by a sinister man in a raincoat and black leather gloves, though he is powerless to do anything to stop him. With a feeling that something is not quite right about the scene he has witnessed and the police's inability to make any progress, he launches his own personal investigation - and nearly loses his life in the process. While this modern day Jack-the-Ripper type is slithering through the dark byways of Rome slicing up pretty girls.