Possible Clues:

• CID officer (abbrev.)
• Spade, e.g., slangily
• Short investigator?
• Spade, e.g., briefly
• Hammett's Spade, e.g.
• Luxury hotel name
• Dick Tracy, e.g.
• V.I. Warshawski, e.g.
• Dick Tracy is one, briefly
• Gumshoe, slangily