Possible Clues:

• Conclusive evidence
• Indisputable evidence
• Damning evidence
• One's been recently fired for criminal activity?
• Unarguable evidence such a jacket needs arm
• Evidence of crime just committed
• Whodunit evidence
• Immediate and irrefutable evidence of crime
• Proof of crime in newspaper - monarch grabbed by cat
• Clear evidence of puffing that's heard at start of race