As Arthur Fleck was such an unreliable narrator, much of Joker is left up to the audience to interpret for themselves. It’s clear in the movie itself that whole scenes or plot threads might have just happened in Arthur’s head and his relationship with his kindly neighbor Sophie Dumond (Zazie Beetz), for example, was entirely fictitious, as revealed when Arthur enters her apartment and she hardly knows him.
This scene ends without confirmation of what happens next though, and some have theorized that Joker killed her, in his increasingly unhinged state, for shattering his illusion. IndieWire put this possibility to director Todd Phillips, and he made clear exactly what Sophie’s fate is.
Phillips explained that there was some additional footage filmed of Sophie watching Arthur on Murray Franklin’s show, which would have confirmed that she lives. However, this was ultimately excised as Phillips wanted to keep everything from Arthur’s point of view. He explained to IW that murdering Sophie would go against this Joker’s personal code, saying:
“He doesn’t kill her, definitively. As the filmmaker and the writer I am saying he doesn’t kill her. We like the idea that it’s almost like a litmus test for the audience to say, ‘how crazy is he?’ Most people that I’ve spoken to think he didn’t kill her because they understand the idea that he only kills people that did him wrong. She had nothing to do with it. Most people understood that, even as a villain, he was living by a certain code. Of course he didn’t kill this woman down the hall.”
It’s an interesting revelation from Phillips that the Joaquin Phoenix Joker only kills those who have wronged him. That’s certainly not true of the typical Clown Prince of Crime, who merrily murders his way through Gotham City in order to get his kicks.
This may play into the enigma of whether Fleck is the real Joker, after all, too. Due to the proliferation of rioting folks in clown masks in the film’s denouement, it’s often thought that he may just inspire Batman’s eventual nemesis. Phoenix himself doesn’t see it this way, but Phillips has previously encouraged people to ask questions like this. One question we don’t need to ponder anymore though is what happened to Sophie?