This is a beautifully filmed and well-written 70s thriller that continually gets darker and sicker. It's one of the darkest giallos I've seen due to the nature of the sadistic nun Gertrude and her descent into insanity and morphine addiction.
The only reason The Killer Nun even qualifies as giallo is because there is a twist at the end, exposing the real killer. However, the director Giulio Berruti chose a true and bizarre Seventies European murder case to exploit, and there's an unsettling contrast between the small, restricted lives of the residents of the nursing home - including the nuns themselves who are repressing various forms of sexuality and/or anger - and the brutality of both addiction and murder.
The only reason The Killer Nun even qualifies as giallo is because there is a twist at the end, exposing the real killer. However, the director Giulio Berruti chose a true and bizarre Seventies European murder case to exploit, and there's an unsettling contrast between the small, restricted lives of the residents of the nursing home - including the nuns themselves who are repressing various forms of sexuality and/or anger - and the brutality of both addiction and murder.