I had first watched this some years ago and recall being underwhelmed by it but, then, that viewing had been accompanied by Avati's much more somber and altogether superior efforts THE HOUSE WITH LAUGHING WINDOWS (1976) and ZEDER (1983)...
A bizarre but heavy-handed giallo spoof whose overall effect is extremely uneven, it features a plethora of eccentric characters: inept detective, diminutive hero, a cross-eyed psycho and a dwarf (actually a man in drag!) for servants plus a mad combo of relatives including a matriarch suffering from dementia, her cowboy of a second husband, her sex-crazed retard son who has to be frequently restrained via electro-shock therapy, another son who's also a 'little man' (played by Bob Tonelli, one of the film's own financiers!), etc. Both the hero and the detective overstate their masculinity the former swaggers incessantly, while the latter is frequently caught with his pants down; the lovely and lively heroine is played by Francesca Marciano (whose character in THE HOUSE WITH LAUGHING WINDOWS was given a particularly gruesome death, a scene which had even adorned that film's memorable poster!).
The film does provide some belly laughs such as the casual knifing of a book vendor early on, the death of a relative by a booby-trap hair-dryer, his wife's demise via a dynamite placed in her mouth, the detective biting Tonelli's hand to check if it's fake (with the latter snapping "F*** You!" at the former's suggestion to try the other one), and the American jumping on his horse from a high window (with the animal ending up half-buried in the ground and the rider with a tremendous pain in the groin!). There's also an ingenious resolution (with the initials of all the victims comprising an anagram of the location of the family treasure's hiding-place) even though the identity of the killer is rather given away by the film's very title!
The Raro DVD edition I watched includes an interesting featurette lasting a little over half-an-hour involving the Avati brothers (co-writer/director Pupi and co-writer/producer Antonio), star Gianni Cavina (the detective) and character actor/TV personality Michele Mirabella (the cowboy) in which they discuss the genesis of the film and its production, as well as their relationship to one another and the rest of the cast.
Ultimately, I liked the movie well enough this time around to want to check out two other Avati comedies I recently taped off late-night Italian TV LA MAZURKA DEL BARONE, DELLA SANTA E DEL FICO FIORONE (1975) and BORDELLA (1975)...