I am wondering more and more whether Jerome was actually meant to be the Joker... Gotham is supposed to be the chronicles of a pre-Batman Gotham, so the stories are more about the back-story of the characters found in the comics. For example, Gerard Crane in Gotham was trying to induce fears in others using toxins / psychology. And in the comics, the Scarecrow aka Dr. Crane has the same MO. When I first watched the episode with Gerard Crane, I first thought that he was the same as the Scarecrow in the comics. But as I did a little more research (my Batman knowledge isn't completely perfect) I realized that that episode was probably much more meant as the back-story to the actual Scarecrow... In Gotham, Gerard Crane had a son who at the end of the episode, Gerard had inflicted his son with the same drugs in an effort to control his son's fears; however the "treatment" went wrong and the son now suffers from a Scarecrow phobia. This son's name is Jonathan Crane, which is the same as the alter-ego of Scarecrow in the comics. Thus I now believe that Gerard Crane was not supposed to be the Scarecrow but rather shows the origin of how his son will eventually take over that villainous role.
Likewise Jerome is probably not in fact the Joker, but is a pre-cursor to who will eventually become the Joker. Remember that Theo remarked on Jermone's laugh, which was shown as the trigger of insane acts of violence by several other people following Jerome's death. Thus I'm thinking that Gotham's Joker is probably someone that is trying to emulate Jerome, including his infectious laugh. Furthermore, Gotham has shown a Red Hood episode showing the exploits of the Red Hood Gang; at the end of the episode, all former members of the gang have been killed, but the hood itself was picked up by a young boy... In the comics, the Joker was originally one of the people to take up the Red Hood mantel; it was while making a heist at a chemical plant where he, while wearing the Red Hood, jumps into a vat of chemicals that leads to the Joker's deformities / coloration as he attempts to escape Batman. So I'm thinking that the Red Hood episode in Gotham was also meant to act as the back-story as to how whoever becomes the Joker originally started as Red Hood (as the boy that picked up the hood in the end of the episode).