BEFORE I HANG is an intriguing little chunk of B-Film that explores the old idea that blood has memory, that the tissues and bones of the criminally insane pulse with a life that makes them who they are. In short, blood will have blood, as Macbeth says after the appearance of Banquo's ghost.
Boris Karloff is strong in this piece about a Dr. John Garth, who is seeking a serum that may alleviate the ravages of age. His experiments have led him to "mercy kill" one of the subjects of his studies, and for this, he is sentenced to death. Offered a chance to redeem himself through medical research in prison, he and a colleague (played by the fine character actor Edward Van Sloan) inoculate Garth with an experimental serum drawn from the veins of an executed murderer. The serum works, but Garth becomes a homicidal maniac. He kills his colleague and a prison trustee, and manages to lie his way into a pardon from the state for his humanitarian efforts. After he gets out, he really has a killer's jamboree.
Aside from the mechanical gesture of touching his hand to the back of his neck whenever one of the murderous fits come on, Karloff creates a character who's pretty sympathetic. Evelyn Keyes as his daughter adds some spark to the melodramatic proceedings. Pedro de Cordoba, piano interludes and all, managed to build a soulful and arresting character who stands out all the more against the general flatness of the Columbia "B" company. All in all, the work holds up, and it's a must see for anyone who admires the efforts of Karloff and some of the other great characters of that era who (time and again) were able to lend some real spark to what would otherwise have been pretty lifeless strips of celluloid.
Review by oyason from the Internet Movie Database.