In a behind the scenes featurette for The Flash, director Andy Muschietti revealed a secret about the film's version of Batman. Michael Keaton returns to the role he revolutionized in 1989's Batman as an older Bruce Wayne who has retired from the superhero life. As Muchietti explains, Wayne hung up the Bat-armor after breaking the character's one inviolable rule: he killed someone. It matches a similar angle adopted by the DCEU movies, where a homicidal Batman is far more feared than beloved by Gotham.
Source：https://www.cbr.com/batman-becoming-killer-not-only-way-lose-himself/
