Sorted, by author...

• Benton, Mike, editor.
  The Illustrated History of Crime Comics...Buy this book
  Dallas, Texas: Taylor Publishing Company, 1993.
  A mother of a motherlode of info on crime comics, lavishly illustrated, and with plenty of dirt on (and pics of) eyes you and I never even knew existed. Highly recommended.
  .
• Dinan, John A.,
  Private Eyes in the Comics...Buy this book
  Boalsburg, PA: BearManor Media, 2003.
  Master pulp historian John A. Dinan serves up arguably the first book specifically on PIs in the comics. A history and appreciation of the tough guy, the deadly dame and the dog in the trenchcoat. Illustrated.
  .
• Gifford, Denis,
  The Encyclopedia of Comic Characters
  UK: Longman, 1987.
  .
• Goulart, Ron, editor.
  The Encyclopedia of American Comics
  New York: Facts on File, 1990.
  .
• Horn, Maurice, editor.
  The World Encyclopedia of Comics
  New York, New York: Chelsea House Publishers, 1976..