I Don't Fool Around — Lawrence Block

Fischer pulled up at a curb and we got out of the car in a hurry, heading for the black Chevy with the people standing around it. The precinct cop made room for us and we went on through. As far as I was concerned, this was just a formality. I knew who was dead and I knew who had killed him. Taking a good long look at the corpse wasn't going to change that.
A rare classic short story by Lawrence Block!