Gas Chamber ? Set or Location ?
the Gas Chamber scenes is it an elaborate built set or a real location ?
imdb says the film was shot on location
The exterior scenes of San Quentin prison are real, but the gas chamber scenes were done on a carefully constructed sound stage.
Apparently the prison officials allowed the director lots of access to the actual gas chamber at San Quentin, apparently even allowing him to observe an actual execution. But they wouldn't let him film inside there. So the director took photos and made lots of careful notes which allowed him to build a very good replica of the gas chamber for filming purposes.