But GP made it clear that the graffiti charge wasn't the target, it was intended to pressure the person involved into turning on a different criminal associate. Ignoring that reality in favor of focusing exclusively on the charge itself seems unhelpful to me.
Extortion for testimony doesn't tend to produce reliable testimony.
"25 to life for jaywalking, but you'll walk free if you snitch" sounds like extortion to me.
If he's an accomplice, them charge him with that, and turn it into a classical prisoner's dilemma. Don't just make up bullshit charges, that's abuse of the justice system.