The Damned Thing(1975)

Overview:

Doctor who lived at the edge of a swamp was found murdered with his neck slaughtered. Investigator, together with a jury made ​​up of local farmers, comes into the doctor's cabin and tries to discover the cause of his death. The two sources may be of any help: a diary of the doctor, and the testimony of a journalist, the doctor's friend, who was with him at the moment of death. Based on the Ambrose Bierce novel with the same name.