His role has been announced. The main actor of '(500) Days Of Summer' will be playing...
Quotes from Filmonic
"Gordon-Levitt will play John Blake, a Gotham City beat cop assigned to special duty under the command of Commissioner Gordon. Cotillard will appear as Miranda Tate, a Wayne Enterprises board member eager to help a still-grieving Bruce Wayne resume his father’s philanthropic endeavors for Gotham."
... a cop. Shoot! I was hoping that Nolan would make him a new supervillain or The Joker (since he looks so like our late Heath Ledger), but hey!