This is the only giallo that Tonino Valeril made more spaghetti westerns with two very decent ones, Day of Anger (1967) with Lee Van Cleef and My Name is Nobody (1973) with Terence Hill and Henry Fonda. Is single one My Dear Killer (1972) is a happy one with a very solid Police Inspector as the also good George Hilton or I only say the other day as The Sweet Body of Deborah. The action is happy along with a mechanical digger at the beginning, with a rather nasty circular saw for a lady sliced and all the time the story of the unsolved abduction and good cinematography and a splendid score from Morricone.
Review of My Dear Killer
