That's such an interesting thing to think about. For me, the biggest difference isn't in the 'what' but the 'why.' Fictional mysteries are built around the story, you know? The author plants clues for the reader, twists are crafted for maximum impact, and everything leads to a resolution that feels thematically right. Even the most chaotic thrillers have this underlying architecture. The detective, whether a cop or an amateur, often serves as our surrogate, piecing together the puzzle that was, from the start, a complete puzzle with all its pieces hidden in the text.
Real-life mysteries, though, they're messy and often don't care about narrative satisfaction. They lack that authorial hand guiding you toward a climax. You're not given a curated set of clues; you're dumped into an ocean of information, most of it irrelevant, contradictory, or missing entirely. The resolution, if it ever comes, might be bureaucratic, anticlimactic, or legally restricted from ever being fully public. Reading a non-fiction account of a true crime case feels more like following a researcher down rabbit holes, hitting dead ends, and grappling with the uncomfortable reality that some threads just lead to a void.
I guess that's why I consume them so differently. Fictional mysteries are for the pleasure of the solved puzzle—that click when the last piece fits. True mysteries are more about the haunting questions, the human behavior, the societal gaps they reveal. One is a constructed game, the other is an incomplete map of something that actually happened, and you can feel that distinction in the pacing and the emotional weight.