Who killed Bruce Wayne's parents?
The suspect list grows ever smaller from established characters.
Joker has been removed.
Penguin, Riddler, and Zasz are the only adult villains. Rest are contemporary age as Bruce. Dick Grayson hasn't been born yet.
That leaves only one adult. Ra's al Ghul. One with motive to cleanse Gotham and motivate someone to be a dark night.
Since the producers have some creative leeway with back story, my money is on the one adult not present at the crime.
Alfred Pennyworth. Such a cliche. The butler did it.
