Revealing mistake: When Blake and Gordon watch Bane on TV during Gotham's siege, a grey (sometimes white) square is reflected on Gordon's glasses. It's either a lighting screen or the proof that the TV is turned off and the image on it is added on post-production.
Revealing mistake: During the party, the second time Gordon gives a speech praising Dent, a lighting screen is reflected on his glasses, which disappears in opposite shots.
Revealing mistake: When Bane first breaks into the stock exchange, he forces one of the guards into shooting his gun. Two mistakes: there is no flash or muzzle flare, and the gun has an insane amount of recoil. It's not a cannon, it's a 9mm. It's also not the guard being startled by Bane: Bane is the one holding his arm.
Chosen answer: Given that no accurate records would have been kept of what occurred in Gotham during Bane's occupation, it would be very easy to claim that Bruce had been in the city when the bridges fell, been captured and subsequently executed by forcing him out on the ice, as had happened with many other socialites. Plenty of people died during Bane's takeover of the city, particularly in the final hours. There's no reason why Bruce would stand out among them as a candidate, and even if anybody did harbour some suspicion, it could hardly be proven.
Tailkinker ★