Police is never quite smart in Batman movies. That's why everyone in Gotham knew the major was going to be the next Joker's victim in TDK. Yet a man with big scars in his mouth was able to get a uniform, a gun and place himself right next to the major and fire at him and nobody noticed. And nobody could notice him AFTER the incident so he could escape without further problem. Not even all those cops in the rooftops could. They could spot a window's curtain opening, but the Joker and his accomplice... no sir. Lousy security there. I mean, at least Penguin didn't announce what was his next move like Joker did. But the same could be said about Harvey Dent being freed by Joker when all the police were guarding the hospital, and what about the bank robbery, everyone saw the School bus coming out from that hole in the bank's wall, the police were even getting there in that moment. But they didn't do anything. See?