And to say that the title already suggested something.
The most ardent fans had immediately seen as curious the choice to call the film "Joker" and not "The Joker".
The film confirms that what we have seen is perhaps the genesis of the Joker as an entity but not of the Joker as a character.
Arthur is not the Joker but he may be the one who will say it. Perhaps the Joker is not a person but an entity, a Banksy entity that embodies an ideal, albeit an evil one, and that makes a mockery of the person who plays the role of the clown, a bit like what happens with the Guy Fawkes mask for the anonymous movement.
So what did we actually see happen?
Who killed Thomas Wayne?
Are Bruce and Arthur brothers?
Murray Franklin really died?
Unanswered questions that we could never understand as the final comment suggests.
But what we have learned to understand very well is why Gotham and only Gotham gave birth to the Joker. Gotham had his hero but gave birth to his antihero well. Joker is the fruit of a sick society, as is often ours. Joker is born where the last ones are always the last ones. Joker lives when he realizes that it would be better to die. Joker proliferates when so many feel robbed and not just a few. Joker represents evil but not evil as an end in itself. Not a bad thing in search of personal revenge in search of redemption. It represents a very sick evil that finds its cure in violence, a violence against who and what generated that evil.
No justification but a crude analysis of evil and illness as such. A film that speaks to us of Joker and not of The Joker therefore, and does it subtly and terribly without fear of disturbing our sleep with that evil and very sick laugh.