Batman wasn't supposed to kill anyone but during the climactic scene of The Dark Knight Rises, he shoots the truck carrying the bomb with The Bat in an attempt to reroute the truck and the driver is killed.
Did Nolan make a mistake here?
Even in The Dark Knight Batman tries to save Gordon's son and pushes Dent from the edge. But accidentally Dent dies. So Batman has his own rules saying not to kill anyone intentionally. In the same way he wanted to divert the truck by shooting but accidentally shoots the driver. So that doesn't mean Nolan as well as Batman makes a mistake.
It was an accident...