Murderer's Vanity (an Amos Lee Mappin mystery) in Bloomington, MN

Crime author Amos Lee Mappin gives a radio interview that catches the ear of a would-be killer, setting up a deadly game of cat and mouse. Will a murder go unnoticed while a psychopath freely walks the streets? Mappin must use all of his wits to piece together a bare handful of clues. Murder will out . . . or will it?
Murderer's Vanity
was published in 1940.