Related Clues:

• Help for a detective
• Rationale
• It may be airtight
• Defense of a sort
• Solver's aid
• Game with Mustard and Plum
• Grafton's A
• Crossword staple
• "I was at the movies," e.g.
• Suspect's explanation
• One might stand up in court
• Suspect eliminator
• Whodunit item
• Intimation
• Mr. Green's game