Case workers, briefly, 4 letters
Clue hunters, slangily, 4 letters
Columbo, Spade, and others, 4 letters
Gumshoes, for short, 4 letters
Hammer or Spade types, 4 letters
Hired sleuths, slangily, 4 letters
Investigators, for short, 4 letters
Investigators, slangily, 4 letters
Private eyes, for short, 4 letters
Private eyes, in slang, 4 letters
Private eyes, slangily, 4 letters
Private investigators, for short, 4 letters
Professional snoops, 4 letters
Spade and Marlowe, briefly, 4 letters