Related Clues:

• Fingerprint or dropped handkerchief, say
• Set the pace
• This, for example
• Detective's need
• Bullets
• Print, maybe
• It may be found with a magnifying glass
• Guiding light?
• Inkling
• Fingerprint, perhaps
• Start off
• Sleuth's find
• Airhead's lack?
• Guide
• Footprint, maybe