Related Clues:

• P.I., e.g.
• Mr. Moto, e.g.
• Peeper
• Dick
• Detective
• One may follow a lead
• Nosy sort
• Nosey Parker
• Sleuth, for short
• Private detective
• Nosy Parker
• Clue collector, slangily
• Sherlock Holmes or Hercule Poirot
• Curious sort
• Old-time gumshoe