The 1967 novel, Ritual by David Pinner, about a police officer investigating what appears to be a ritualistic killing in a rural English town, was the basis of this film. SPOILER ALERT: In the novel, the townspeople don't seem to know what happened, largely because it turns out the police officer, a schizophrenic devout Christian, was the killer all along. Thus, the ending differs greatly from this 1973 film which was inspired by that novel, in which the police officer, played by Edward Woodward, ends up the victim in a May Day related ritual which wasn't in the novel, but which was created for the film based on the writings of Julius Caesar while he was in Gaul. Identify this 1973 film which featured an occasionally nude and prancing Britt Eklund.
The Wicker Man