Similarly, does Joker kill Thomas Wayne?
Joquin Phoenix's Joker doesn't kill Bruce Wayne's parents outright, but he does create a lawless situation that basically causes it to happen. Toward the end of the movie, this version of the Joker has several Joker minions, and a guy in a Joker mask kills Thomas and Martha Wayne, in front of 10-year-old Bruce Wayne.
Subsequently, question is, why was Thomas Wayne killed in Joker? Fleck's mental problems or at least exacerbated them, which fueled Arthur's problems and his descent into becoming Joker which inadvertently caused Thomas Wayne's death, which of course sends Bruce Wayne on a life-long mission of vengeance.
One may also ask, was Thomas Wayne The Joker's dad?
You have been warned! In Joker, Thomas Wayne (Batman's father) and Penny Fleck (Joker's mother) are key characters. Penny claims that Thomas is actually Arthur's father. The movie wants you to guess for yourself who's telling the truth.
Did Batman ever find the man who killed his parents?
In 1989 in the Batman movie Batman discovers the murderer of his parents is Jack Napier who later became the Joker. There was no indication that Napier had a non-random reason but then he was the proto-Joker. Then in 1994 it was decided to change things so Batman never identified his parents killer.