This question was prompted by watching The League of Extraordinary Gentlemen. In Venice, the crewman gasps, "It was Grey, not Skinner", and dies.
Various aspects of the screenplay and score suggested this was intended to show a genuine deathbed disclosure. Also, the dying person was a non-prominent crewman, further reducing the chance of an ulterior motive since they had no real role except to be the one gasping a deathbed disclosure (as seen by an audience, even if Grey hadn't actually been shown doing the murder in previous scenes).
We tend to assume that a person dying has nothing to lose, so we place a lot of reliance on such scenes. They are almost always treated as reliable, unless the dying person has been shown to have some strong motive for a deathbed lie. But they need not be — the dying person may believe that if they maintain the lie, and mislead at death, something they want will be done after their death. It might be something they have been coerced into, or a religious or other belief. It could simply be that they held an erroneous belief and passed it on, believing it to be true.
Has there ever been a film with a comparable scene, where the deathbed disclosure was specifically signified by the film score and screenplay, as "genuine", yet part of the plot twist was, that it wasn't?
An ideal 'find' would be where the death was apparently a redshirt — someone who existed purely for the purpose of their deathbed/death scene disclosure, with no/little visible backstory — like in this scene, with the score and screenplay all suggesting veracity, but was in fact misleading.
Example: Without restricting answers, suppose The League of Extraordinary Gentlemen's crewman had untruthfully fingered Mina Harker as he died, instead of Grey, for posthumous revenge reasons only disclosed much later, and with unchanged presentation. More pointedly, suppose he mistakenly thought — and incorrectly told the others — that it was Grey, as he died.