On the DVD commentary, Kevin Conroy admits that he had never read about the Dark Knight until he originally auditioned for the part back in 1991 on Batman: The Animated Series (1992). When he was told the back-story of murdered parents and a quest for revenge, Conroy, who was a trained Shakespearean actor, thought they were telling him the story of Hamlet.
According to Kevin Conroy on the DVD commentary, when they originally did Batman: The Animated Series (1992), they recorded the voices first, and then did the animation. However, for this project, the animation was already done, and the actors had to match their voices with what was seen on the screen.
Originally, they were going to select another actor to play the part of the younger version of Bruce Wayne. However, Kevin Conroy convinced them to give him a chance, and they decided to use his voice instead.
The cover advertises this film as the first Batman animated movie to be rated PG-13. In fact, this is not true. Batman Beyond: Return of the Joker (2000) was the first animated Batman film to carry the rating. Originally edited into a PG rated film, it was later released as an unedited Director's Cut with a PG-13 rating.
According to O'Neill, Lucius Fox was originally a throwaway character, however, in the last ten years, his role has been increased in the Batman story-lines to where he is the one responsible for creating many of Bruce's fancy gadgets.