The Abominable Dr Phibes (1971)

It isn't until there are a handful of victims that Detective Inspector Harry Trout with Scotland Yard believes there is a serial killer on the loose, all the victims physicians and all having been killed in some gruesome, seemingly ritualistic manner somewhere they would have considered safe. The one connection the victims has to each other is to another physician, Dr. Vesalius, who is further able to narrow down the connection to one case, that of Victoria Phibes, Vesalius the chief surgeon with Mrs. Phibes having died on the operating room table. Her body was subsequently interred next to her husband, musicologist Dr. Anton Phibes, who, in rushing to the hospital upon learning that his wife was there, died in a fiery car crash en route, his body incinerated on the spot. With further evidence coming to light, Trout and Vesalius believe that all on the medical team on that case, including Dr. Vesalius, will be targets of the killer, whose method of murder is each of the Ten Plagues of Egypt in some form, with Vesalius most likely the last in being "the prize". As Trout and Vesalius try to stop the killer in knowing the targets and the method of killing, they still have to discover who the killer is, one incredulous thought upon which they are working being that Dr. Phibes is somehow orchestrating it all from the grave.