Possible Clues:

• Sleuth, in old crime fiction
• Philip Marlowe type, informally
• Investigator regularly observed in the act
• Investigator doesn't finish college
• Investigator's hours out of college
• Private Eye shortly gets half of 27 down
• Private eye, in old lingo
• Detective, slangily
• Columbo, for one
• M.Hammer or S.Holmes