Everyone needs to understand that the person who killed his mother in this episode was not the Joker. The Joker has no alias. He has never been given a "real name" in the comics. The Riddler is Edward Nigma, the Penguin is Oswald Cobblepot , Two Face is Harvey Dent...the Joker is only the Joker. His back story is that he was a failed comedian, who started working for the mob on the side for extra income. He failed a job he was given and was set up to die at a chemical factory. He survived, somewhat, to return home and find his wife murdered. The joker appeared in the very first episode of Gotham. He was the comedian trying out in Fish Mooney's club. Notice how he wasn't funny and he is not given a name. Hope this clears things up for some.
