An early black comedy- SPOILERS
DON'T READ THIS IF YOU HAVEN'T SEEN THE MOVIE YET.
McGinty prospers as a politician only for as long as he is crooked. Out of love for a good woman he goes straight, and is immediately punished. You might say it anticipates Kind Hearts and Coronets in which the protagonist gets away with many murders and is finally convicted and sentenced to hang for a death he had nothing to do with.