You-- you strangled O'Brien with his belt, then you got Beatty to come over, and you did the same thing to him. Then you tied the belts up, and pushed them down, and made them look like they hung themselves.

The wardens found enough evidence at the scene to know that it was you, and when Beatty and O'Brien come back they'll confirm it. Now tell me if you remember why you did this, please?