Boris Karloff starred in a number of mad scientist programmers concerning the resurrection of the dead, and the 1939 example THE MAN THEY COULD NOT HANG is no better or worse than any of them. It is what it is, a studio B picture that straddles the mystery and horror genres, buoyed by the lead performance of a name actor.
Karloff stars as a doctor working on an experimental mechanical heart, which he believes will help prolong life. With an unusually game lab assistant, who volunteers to be put to death in order to test the heart, Karloff finds himself facing a murder rap when his nurse interrupts the procedure and causes the assistant to die before the heart can be fitted. (I don't know what medical protocol was like during the '30s, but Karloff could've saved himself a world of trouble if he'd gotten his lackey's consent in writing.)
Dismissed as a murderer and not the visionary groundbreaker that he sees himself, Karloff is sent to the gallows by a typically closed-minded jury. But thanks to the help of a colleague, who uses the prototype heart to bring him from the dead, Karloff will be able to settle the score.
The biggest problem with HANG is that it's all build-up with little pay-off; Karloff doesn't even see the noose until past the mid-point, and even then it's conveyed as a series of news headlines. Once Karloff begins his revenge we're told six jurors have been found hanged, but all of this potentially interesting material is transmitted secondhand. (It doesn't help that director Nick Grinde presents the film as visually unremarkable as possible, keeping the production half a notch above the average Poverty Row potboiler.)
What the film chooses to dramatize is the remaining members of Karloff's trial being called to his mansion for the culmination of his revenge. It's supposed to feel like an Agatha Christie mystery, but the action is too awkwardly staged and more than a little silly, not to mention incredulous. Karloff's vengeance lacks bite, and the drawing-room antics are over before they gather any momentum (topped with a schmaltzy ending that probably had 'em groaning back in '39).
Though I'm glad vintage horror films are getting a new audience on DVD, it's a shame that lesser movies like this one are getting released over more accomplished fare like THE WALKING DEAD (a much better living dead/mad scientist movie from 1936 also featuring Karloff). Too tame to entertain horror fans, and too straightforward for mystery audiences, it occupies a strange middle ground that will please only Karloff aficionados or undiscriminating fans of classic cinema.