Murder on Diamond Row

Who's hand writes these messages of death?

London's jewel thieves are under the thumb of a mysterious fence, who ruthlessly exposes any thief who crosses him. Desperate, Scotland Yard re-hires ex-Inspector Barrabal who, as a known drunkard, is ideally suited to go undercover with a faked criminal record (which may spoil his chances with lovely Carol Stedman). Interested parties: Larry Graeme, cat burglar; his girl, sexy dancer Tamara; Collie, sardonic reporter. Then murder makes apprehension of the Squeaker urgent.