What direct-to-films series features Batman: The Killing Joke?
Batman: The Killing Joke (film):  Featuring the DC Comics character Batman, the film is the twenty-sixth film in the DC Universe Animated Original Movies series, based on the by Alan Moore and Brian Bolland. DC Universe Animated Original Movies: The DC Universe Animated Original Movies (also known as DC Universe Original Movies) are direct-to-video film projects being created by Warner Premiere, Warner Bros.
DC Universe Animated Original Movies