Not sure if anyone has mentioned it, but I don't see anything about the the ending of this movie. Why did Batman take the fall for all of this? Maybe I missed something, but couldn't they have blamed those murders on the Joker instead of Batman? The people of Gotham certainly would have believed that after all of the shit he put them through. Everyone in the movie is conveniently stupid as hell as it is.
The Joker was already captured when Harvey Dent was killed by Batman. Whilst Harvey was killing people Joker was on the news or blowing up various boats.
They had to frame Batman for Dents's death, they may as well say he killed the others to keep it simple. If they said Joker did it and one person can show a picture or threat from the Joker somewhere else they would be found out. Batman has always been hidden, they didn't know where Joker was during the deaths so they don't know if anyone could confirm his location etc. It would be VERY risky framing Joker.
The police commissioner could confirm Batman did it. As well as there being several cops and probably cameras seeing Batman run from the scene.