Look, this show isn't strong enough for me to hold any acute objections to it tackling The Joker. Given the problems the series has at its core, Joker is not suddenly something I'm now demanding they "do right." But I am intrigued about how things are supposed to piece together for him. If Jerome was supposed to be Joker, then his origin story happened years ago when something made him snap. So it's very likely that he's just a random(ish) psycho (who the previews for the episode made sure to show us being psycho, thus ruining the entire murder mystery).