Yeah, the shooting is the main thing here.
As a Batman fan, I hate this because all the anti-Batman ppl get on some BS talking about "Heath Ledger's death is what made TDK gross so much". No, dummy, the fact that it was a great movie with a lot of hype was the reason it made so much money.
The midnight showings of TDKR outsold the midnight showings of The Avengers...so WHY is TDKR lagging behind the Avengers (besides the lack of 3-D)? It's like everyone is saying...the largest mass shooting in US history turned a LOT of casual moviegoers off of seeing it.
Even with that, it's still the second highest grossing movie this year.