What Detective Black should have done.

He should have never called the SWAT team for help. Just spy on the girl on his own. Then if the killer shows up, just shoot him.
His story could have been that he was there with the girl and he had to go pee. When he got back the killer was attacking her so he shot him. Case closed.
If the Wizard doesn't show up; then I am sure the next day that car crash would be the talk of the town and Det. Black would have found out that Oliver works at a candy shop. On his way to investigate the candy shop....he finds out that they sell chocolate Porcupines. Case closed.