Regardless of genre or plot leading up to the end, if the villain (or murderer, as the case may be) has to explain what they did and why, possibly in a Just Between You and Me, then you did something wrong. Evidence should be presented to the viewer as to what's going on, even if it's important that the protagonist/detective never figures something important out.
I greatly dislike getting all of the necessary information to understand the plot in a villain monologue in the last 5% of the narrative. It's highly irritating.
That said, the only mystery I've ever written (...am writing...) is highly unorthodox to begin with (fake detective [who dies three chapters in], time loops, watching people who are otherwise good guys kill everyone, etc.), so I don't think I've ever been in a position to write something in the way of a closed-circle mystery and dodge such... mistakes.
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I greatly dislike getting all of the necessary information to understand the plot in a villain monologue in the last 5% of the narrative. It's highly irritating.
That said, the only mystery I've ever written (...am writing...) is highly unorthodox to begin with (fake detective [who dies three chapters in], time loops, watching people who are otherwise good guys kill everyone, etc.), so I don't think I've ever been in a position to write something in the way of a closed-circle mystery and dodge such... mistakes.