Factual error: In the cemetery, the skeleton of Gregory Peck's son is far too big to be that of a newborn, which it is supposed to be.
Other mistake: Although the Lieutenant is actually sent to the police station in precinct 9, division 13, the sign over the door states it to be division 14.
Continuity mistake: Right at the end when the man takes his mask off, a strand of blonde hair hangs out from the back of "his" head. In the next shot the hair is dark brown.
Visible crew/equipment: As Mario emerges into the house from the rain to get the bodies, a crew member is seen when he opens the second door. (01:04:05)
Revealing mistake: At the pork processing plant, a close-up from an Italian newspaper "Corriere della sera" shows news from November 18, when it's established from previous conversations that the killer was captured on November 30th, so it should be a December newspaper. (00:53:00)
Other mistake: Legendary wrestler Antonino Rocca makes a cameo appearance in the movie. He is, as correctly listed in the closing credits, one of the "Funeral Attendants" together with Michael Weil. However in the opening credits he was specifically billed as the Funeral Director, which is Ronald Willoughby's role as correctly listed in the end credits. (00:00:50 - 01:45:15)