The police knows 6 people escaped Arkham, so why only give the profile for 5 of them at the briefing? They couldn't have known one already died.
Jerome taps on the window of the bus with his revolver and you can clearly see all the chambers in the cylinder are empty. Moments later he is seen firing the revolver through the roof of the bus.
An interior shot of the bus after Jerome says, "light 'em up" shows everything and everyone inside to be dry, even though it had been hosed down inside with gasoline moments before.