Joker might have come out last year, but its fans are still poring over every detail in the celebrated DC movie for new theories.
A lot of what happens in Joker is left deliberately ambiguous such as that ending, but there's also one key detail about Arthur Fleck's history that we're left to speculate over: why was Arthur in Arkham before?
But now a new theory from Reddit user DecoyThylacine has offered a solution to the mystery – and it's not a happy one.
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Related: This Joker theory will make you view the DC movie in a different light
Early on in the movie, we see Arthur at one of his appointments with a social worker and she asks him how it feels to have these kinds of meetings.
"I think I felt better when I was locked up in the hospital," Arthur responds, so she asks: "And have you thought more about why you were locked up?"
We get a brief flashback of Arthur banging his head violently against the door of his cell and instead of an explanation of his time in Arkham, Arthur just replies "Who knows" to her question.
The theory suggests that he was actually in Arkham because he'd let the Joker side of his personality out before, and if that was the case, then it's not a stretch to imagine Arthur might have killed before.
"It's a very strange response that nobody has seemed to pick up on. You either have thought about why you were locked up or you haven't. It's the only time Arthur is obviously being ambiguous. He clearly didn't want to talk about it," the theory reads.
"Maybe he'd already done Joker-like behaviour previously, was locked up, let out after he 'got better', and was put on seven different medications which stifled the Joker side of him that previously put him in Arkham."
It would then raise the question of why he was let out of Arkham if he had killed before, so perhaps Arthur's earlier Joker incarnation didn't actually murder anyone, but showcased dangerous behaviour.
Either way, the theory tracks with what we see play out later in the movie.
Arthur had already killed the Wayne Enterprises businessmen on the subway, but that murder was (largely) self-defence. It's the start of his descent to becoming the Joker, yet it's not until Arthur stops taking his medication that he fully becomes the Joker.
We do actually get a slightly clearer explanation for why Arthur was originally in Arkham in an earlier script for Joker.
Instead of Arthur's "who knows" response, he originally said: "Well I suppose I was mentally ill... Well my mother thought I was mentally ill, so she had me committed."
The social worker then asks him if he felt mentally ill, leading Arthur to respond: "They've been saying that since I was little. So who knows."
But since these lines were taken out of the movie and replaced with the more ambiguous "who knows", it means it's not the official explanation so we can still speculate on Arthur's backstory.
And the suggestion that Arthur has let the Joker out before just seems to make so much sense.
Joker is available to buy on DVD, Blu-ray and 4K Ultra HD, and is also available to watch on streaming.
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Movies Editor, Digital Spy Ian has more than 10 years of movies journalism experience as a writer and editor. Starting out as an intern at trade bible Screen International, he was promoted to report and analyse UK box-office results, as well as carving his own niche with horror movies, attending genre festivals around the world. After moving to Digital Spy, initially as a TV writer, he was nominated for New Digital Talent of the Year at the PPA Digital Awards. He became Movies Editor in 2019, in which role he has interviewed 100s of stars, including Chris Hemsworth, Florence Pugh, Keanu Reeves, Idris Elba and Olivia Colman, become a human encyclopedia for Marvel and appeared as an expert guest on BBC News and on-stage at MCM Comic-Con. Where he can, he continues to push his horror agenda – whether his editor likes it or not.
