"I have this awesome ghost gun that's basically impossible to trace back to me, so of course I think I'll hold onto this instead of ditching it, but I'll take the time to ditch this here backpack in central park."

You'd have a hard time convincing me that the cops didn't find the gun in that bag and wait to plant it on the first believable suspect to pop up. They had zero leads before that phone call came in, and they're stiffing the rat that called out of that reward money they promised. They just needed to be able to say that nobody gets away with eating the rich.