I'm looking for books where there is a mystery that can be solved by reading various documents, letters, interview transcripts etc. like The Appeal by Janice Hallett. Books like Tokyo Zodiac Murders where people investigate a famous (fictional) case that happened in the past by interviewing people and reading letters written long ago are also welcome. I don't think these count as epistolary though.
It's better if the mystery can be solved by bringing various pieces of information together rather than a single revealing clue at the end.
I'm not a fan of mentally ill protagonists (in terms of memory loss or visions) or unreliable narrators. Of course in these types of novels there will be lying interviewees and such but I prefer having a reliable reference point.
I'd prefer if the mystery isn't too personal for the investigator. For example, ideally, the killer shouldn't be the detective's ex wife's husband.
by HulaguIncarnate