An early example of a novel which is told through flashbacks and conversations about the past

This came out of a discussion at r/agathachristie, about "Five Little Pigs" (1942).

This Poirot story involves a murder which occurred 14 years before the opening of the story (I think they're called "cold cases" now). Poirot is then engaged to solve this mystery. He does so via a series of conversations about the past from the people involved.

So someone commented this is the first time somebody wrote a novel like this, as far as they know. I am not a literature expert, but probably someone here would know if this is true? It might be, but also, maybe not? Maybe it is one of the more successful examples of a story told through conversations about the past? The novel was pretty well-established as a genre by 1942, right?