From Buzzfeed, an advance look at Batman Earth One by Geoff Johns and Gary Frank. Including this revalatory question…

BF: It was interesting how you showed the death's of Bruce's parents. The moment is so iconic, but as far as I know, no one gone into the immediate aftermath of what happens when a 10 year old watches his parents get shot in the street. Did that grow organically while you were storytelling or did someone on the team have a moment where they said, "We should probably go into how that would be psychologically traumatizing to a child and warp their world view."?