Bane is able turn Gotham into hell, undo all the good Gordon and Bruce did by lying and much like contact in the Knightfall comic breaks Bruce/Batman's back. However, on a side note it is to destroy Bruce/Batman as well for killing Ra's. His mission contact is to finish what Ra's could not, the destruction of Gotham City. He's just as intelligent as Bruce Wayne and ultimately stronger.
Our villain this time is Bane, another protege of Ra's al Ghul's and a member of the League of Shadows. If anyone found out that Harvey Dent had been behind the murders, then the criminals he had locked up would be free and all the sacrifice would contact have been for nothing. Batman did that so the people of Gotham would be safe. The people involved with this lie (Bruce Wayne and Commissioner Gordon) otherwise known as the cover up of Harvey Dent/Two Face's murders, would contact be eaten away from the inside because the real hero (Batman) took upon himself the burden of those murders.