I am a fairly dyed-in-the-wool crime fiction fan. I am also, by training, a historian. Those two interests are not at all disharmonious - all history involves an element of speculation, of reconstruction, of imaginative forensics if you like. (I don't believe in the notion of objectivity in history - or, for that matter, in fiction. The subjectivity of the writer is always there and always influential in shaping the presentation of the story, whether it's factually based or not).
Aside from any methodological symmetries, history is, of course, rife with actual, literal, mysteries; crimes unsolved (or solved unsatisfactorily), secrets half-discovered, motives unexplained or bizarre. Recorded history is a rich vein for novelists and conspiracy theorists alike (hello, Dan Brown) and it is an enormously popular one at that.
When really good writers combine history and mystery, the results are, to my mind, one of the most entirely satisfying reading experiences. (I don't mean mystery novels set in historical periods here, although there are many those I love too - I mean books that take on actual historical conundra). I've read a lot of so-so books in this genre, but three of my absolute favourites are PD James and TA Critchley's The Maul and the Pear Tree; Colin Dexter's The Wench is Dead; and Josephine Tey's wonderful novel The Daughter of Time, which I read for the first time before Christmas and was left amazed (and wondering why it had taken me so long to get to it!)
The Maul and the Pear Tree (1971) is mystery author PD James and historian TA Critchley's re-examination of the 1811 Ratcliff Highway murders. Although lacking the modern fame of the Jack the Ripper killings (and oh, what an industry those crimes have spawned), the Ratcliff Highway murders were nonetheless, in their time, among the most shocking and brutal crimes on record, causing massive public outcry and panic. The crime wave came in two parts. First, a young London draper, Timothy Marr, his wife, Celia, their 3-month-old son, Timothy, and teenage shop boy, James Gowan, were murdered in a short space of time within their shop / home, while their servant, Margaret Jewell, was out seeking to buy oysters. Twelve days later, a local publican, John Williamson, his wife, Elizabeth, and their servant Bridget Harrington were slaughtered in their pub, while the Williamsons' 14 year old grand-daughter Kitty slept through the whole thing and was unscathed. There was a fifth person in the house too: a lodger, John Turner, heard the crimes in progress and escaped out a window by knotting together some sheets (a panicked reaction that strikes me, even at this remove, as entirely human and understandable, if not particularly admirable).
What I found so engrossing about this text the first time I read it was its seamless integration of the solid and detailed historical scholarship of Critchley - the research is impeccable - with the deductive and creative brilliance of James. I have read many true crime books that either are badly, sloppily researched (and usually make overdrawn claims from inadequate evidence) or which, on the other side, plod along without ever weaving a coherent narrative, not brave enough to make deductive (and, necessarily, unprovable) leaps in order to come to a conclusion. The Maul and the Pear Tree is gripping, chilling, and convincing because it is neither light on historical fact nor beholden to it.
The Wench is Dead (1989) is, in my opinion, the very best of a very good series - Colin Dexter's Inspector Morse books. Following the literary device employed so successfully by Josephine Tey thirty years earlier (see The Daughter of Time, below), the plot revolves around Dexter's detective, Morse, lying in a hospital bed, bored, and becoming intrigued with a historical mystery. (The case that Morse investigates is based on a real murder case from the 1830s, the murder of a woman named Christina Collins, but Dexter changes names, facts and details to adapt the case more fully to his plot - unlike The Maul and the Pear Tree, this is not a "straight" historical mystery investigation).
It's a reasonably little book - no chunky tome here - but it is such a gem. Morse's interrogation of documentary evidence, using his detective abilities, is a joy to read and completely satisfying in its denouement. The evocation of life on the canals is utterly wonderful. I've read this book time and again since first encountering it in the 1990s, and it never disappoints.
The best of them all, though, is the oldest - Josephine Tey's 1951 book The Daughter of Time, in which she uses her bed-bound detective, Alan Grant, to investigate, reason and argue the case for Richard III as a spectacularly maligned historical innocent, rather than the nephew-killing monster of popular (Tudor-era and modern) mythology.
What I love - adore - about this text is how Grant and his helpers come to understand and explain how history is made. Not how things happen - that's not history, that's just things happening. Rather, history, in the sense it's used here, is the authoritative account of what happened, the approved picture of events, the received wisdom, the things everyone knows about what happened (even if it didn't actually, well, happen). The title of the book is taken from a quote from Francis Bacon: "Truth is the daughter of time, not of authority." This book is the quintessential and wonderful epitome of this idea.
(As well as loving it, I'm convinced by it - unless a persuasive case is made in the other direction, I think Tey's made the default understanding to be that of Richard's innocence and quite amazing slandering, not guilt, with this effort).
So, if you are a mystery fan or a history fan (but especially if you're both), these three will all repay your time most handsomely.