Possible Clues:

• That's as dirt comes in threes
• One might attempt advertisements, by the sound of it, for such literary forms
• After sound of shot, notices groups of criminals
• Organised raid in backstreet exposes Chinese criminals
• Simple piano chords
• Criminal fraternity from the East found presumably in 11 down
• Cadence components, sometimes
• Sheet music threesomes
• Dart is thrown in sets of three
• Chinese crime syndicates