Related Clues:

• It may be airtight
• Defense of a sort
• "I was at the movies," e.g.
• Suspect's explanation
• One might stand up in court
• Suspect eliminator
• Explanation
• Crook's cover
• Exculpatory evidence
• Innocence indicator
• It eliminates suspects
• It should be airtight
• Saving yarn?
• Out, of sorts?
• Whodunit plot element