The Haunted Strangler 1958 (aka..Grip Of The Strangler..The Judas Hole

The Haunted Strangler (also known as Grip of the Strangler and originally titled The Judas Hole) is a 1958 British horror film directed by Robert Day and starring Boris Karloff, Jean Kent, Elizabeth Allan, and Anthony Dawson.
It was adapted from "Stranglehold", a story which screenwriter Jan Read had written specially for Boris Karloff, and was shot back to back with producer Richard Gordon's Fiend Without a Face (1958), with both later being released as a double feature by MGM.
In 1860, Edward Styles is accused of being the notorious Haymarket Strangler, who brutally killed five women by partially strangling them with one hand before stabbing them to death. Styles, who lacks the use of one arm, is tried and executed for these crimes. As his coffin is nailed shut, an unknown onlooker slips a knife into it.
Twenty years later, James Rankin, a novelist and social reformer, launches a private investigation to prove that Styles was innocent and would not have been convicted if adequate legal representation had been provided for him at trial. Police official Burk permits Rankin to examine the case evidence. Of note, the Strangler murdered his fifth victim, a dancer named Martha Stuart, at the sleazy Judas Hole music hall, where singer Cora Seth and other witnesses noticed his disabled left arm as he fled the scene; the Strangler's knife was never recovered; and a doctor named Tennant conducted the autopsies on all five Strangler victims as well as Styles, and then fell ill during Styles' burial.
Tennant becomes the focus of Rankin's inquiry. At the hospital where Tennant was brought, Rankin learns the doctor had been diagnosed with a severe nervous breakdown and was going to be institutionalized, but he and his nurse both vanished without a trace. Rankin takes possession of Tennant's abandoned personal effects, which include a journal containing unusually detailed descriptions of the Strangler's victims and a surgeon's kit with a missing knife. At the Judas Hole, Rankin gleans from Cora that she never saw the Strangler's face, and that Tennant was a regular patron who made unwanted advances towards Martha Stuart. Rankin deduces that Tennant was the real Haymarket Strangler, and suspects that his breakdown was precipitated by him disposing of his knife, the symbol of his homicidal compulsion, in Styles' coffin in a lucid moment when he was overwhelmed by guilt.
Rankin next goes to the Newgate Prison cemetery and surreptitiously exhumes Styles' body. Finding the knife amid the bones, he takes hold of it and undergoes a transformation that contorts his face, paralyzes his left arm, and alters his personality. Rankin returns to the Judas Hole and kills Cora's protege, and as he departs, Cora recognizes him as the Haymarket Strangler. Alternating between himself and the Strangler persona, Rankin murders other women before finally coming to realize that he was Tennant all along. His wife Barbara confirms this, revealing that she was his nurse etc....