Wait, that's how it happened in the comics? Ok, that's bullshit. I prefer the explanation given in Batman: Under the Red Hood (most recent Batman animated movie). In that, Ra's al Ghul stole the body and had it replaced before it was buried, then dumped it in a Lazarus pit to resurrect it. However, Jason Todd came back a bit deranged and the movie is basically about him getting back at Batman for failing him.