This is indeed a very good little film in spite of the occational dead spot in the film's middle section. It has a very nice atmosphere and some good twists at the end, and I really love the soundtrack; particularly the song "Ho bisogno di te", which is performed in the nightclub. I also believe that this film may have had some influence on the many later 60s gialli featuring Carroll Baker.
It's just too bad that it's so incredibly obscure because it really deserves more appreciation that it's been getting - as does the same year's DEATH ON THE FOURPOSTER, which also features John Drew Barrymore and Luisa Rivelli. Rivelli, btw, is a criminally underrated Eurocult starlet (probably because she got out of the movie business in the early 70s) but she's definitely someone to check out because she's a very talented, sexy and versatile performer.