We're in a dark room, camera panning upward. It's a man strapped to a chair, we've seen this man before, very briefly but he was one of the criminals that was taken out by Batman (I think it's pretty safe to assume there would be some of these criminals in the film).
Criminal (nervously): "No man, please, no, I-I-I swear, I don't know who's at the top of the chain"
Masked man (hidden from camera) drags knife down the side of his face, squeezing into cheek: "Oh I know you won't talk..."
Camera turns to reveal a red bat on his chest, as he moves into the light we come to know who is...Red Hood!
Red Hood (continuing): "...but you will send a message"
Screen goes black as we hear the criminal screaming in pain.