Before I Hang

Before I Hang is a 1940 American science fiction, horror film released by Columbia Pictures, starring Boris Karloff. The film was directed by Nick Grinde under the working title The Wizard of Death, and was one of several films Karloff starred in contract with Columbia.

As he awaits his execution, Dr. Garth is allowed to continue his experiments, thanks to support from the prison warden Ben Taggart and another scientist who is interested in his research, Dr. Ralph Howard Edward Van Sloan. Using the blood of a recently executed prisoner, they succeed in developing a serum that will reverse the effects of aging and they decide to test it on Dr. Garth immediately prior to his execution. As he is being taken away to the gallows, however, the prison receives a call informing them that Dr. Garths sentence has been commuted to life imprisonment. At the same moment, the serums effect on his body causes Dr. Garth to collapse.When Dr. Garth awakes in the prison medical ward, he discovers that the serum has reversed some of the effects of aging on his body, including the graying of his hair, the appearance of his face, and his physical fitness. Encouraged, he decides to perform another test of the serum, this time on Dr. Howard. As he is preparing Dr. Howard for injection, however, Dr. Garth is overcome by a sudden urge to kill, induced by the presence of an executed murderers blood in his system. After he strangles Dr. Howard, a wandering prisoner enters the room who, after a struggle, is also killed by Dr. Garth. ........

Source: Wikipedia