Riddler waves a hand dismissively, clearly not considering murder to be that big a problem. "Don't worry, there's no evidence of it. No bodies, no blood, no bullets. I'm very good at clean up, and Ed's possibly better. Nothing will trace back. And it was the Down, I doubt anyone bothered investigating."

Anyway, it happened because of something the city did to Oswald, that makes it their fault and problem. Clearly.