We still do not fully know when the Joker solo movie will take place on the overarching DC timeline, but if it’s an origin movie then we can reasonably assume that it takes place fairly early within the chronology of the Batman mythos, which means someone like Falcone (or even Salvatore Maroni) could still be around to give some orders to mob thugs.
Before Bruce Wayne returned to Gotham City after his years training abroad, a traditional mafia existed in DC’s most crime-ridden city.
At the head of it all was none other than mob boss Carmine Falcone, who ruled the underworld with an iron fist before The Bat arrived to systematically deconstruct it.