The main point of reading most mystery novels is to find out whodunit, whether the "it" is a murder, a theft or some other crime. And of course, we mystery novelists want the reader to care whodunit. We also know that readers want closure. The mystery readers I know form hypotheses about who the guilty party is, and they want to find out if they were right. So a very important part of any mystery novel is what I'll call the "cards on the table" part, where all is revealed (the murderer, the motive, and how the murder really happened).
I call this "cards on the table" for two reasons. One is that the phrase, "cards on the table" refers to revealing all one's cards in a card game, keeping nothing back. The other is that it's the title of a fascinating Agatha Christie novel (which I recommend). In the novel, Hercule Poirot and three other sleuths combine forces, in a way, to find out who has killed the very eccentric host of a dinner party to which all of the sleuths have been invited. The four sleuths agree to share all of the information they get - to lay their cards on the table.
Some authors lay the cards on the table fairly quickly. The reader knows right away who the murderer is. Daniel Silva's The Kill Artist is like that. So are several Robin Cook novels (Chromosone 6 is an example). In this kind of novel, the enjoyment of reading - the suspense - lies in following the cat-and-mouse game between sleuth(s) and culprit. If it's done well (and both of these authors do it well), such a novel keeps the reader engaged right to the last page.
Other authors have the sleuth slowly figure out who the murder is. Those cards are laid down, you might say, one by one. Many novels fall into this category, actually. K.C. Constantine's Mario Balzic series, Caroline Graham's Inspector Barnaby series, and Rita Mae Brown's Mrs. Murphy series are in this category. So is Joan Smith's Loretta Lawson series. The beauty of this kind of approach to laying down the cards is that it lets the author surprise the reader. For instance, in Patricia Cornwell's Body of Evidence, we follow Kay Scarpetta as she finds out who's behind the murder of author Beryl Madison and her mentor. The reader follows Scarpetta as she pieces the clues together and discovers the murderer - almost too late to save herself. This approach can also be very suspenseful, so long as the style is engaging. Cornwell's is. So is Graham's.
Another way to engage the reader is to hold all the cards back until the end. Agatha Christie was a genius at this. Her Hercule Poirot has often said that he likes to keep his deductions to himself, lest he be wrong and lead others astray. Of course, he is also accused of liking the attention that comes from revealing the murder in a dramatic way. Less flamboyent, but just as reticent at times, is Miss Marple. Marple asks gentle, leading questions, offers hints and guides the reader in her own way, but she, too, doesn't reveal what all of the clues mean to her until the end of the novel. The most engaging thing about this approach is that it allows the reader to match wits against the author. It allows the reader to sift through the clues, try to make sense of them and see where it leads her or him. To me, this pays the reader the respect of assuming the reader can figure things out. I like that.
My own approach is a bit eclectic. Like Christie, I like to give the reader clues throughout the novel. Also like Christie, I explain everything at the end. But my own sleuth, Joel Williams, doesn't save his deductions for the end of the novel. Nor does he give an explanation of his thought process, as Hercule Poirot and Miss Marple do. Instead, he works with the Tiilton Police to make sense of clues as they get them. In that way, my writing is a bit more like the second group of authors I mentioned - Graham, Cornwell, Brown and Constantine. I like to give the reader the closure that comes with an explanation of how the murderer gets caught. At the same time, I do like to let the reader make her or his own journey to the truth. Eclecticism just seems the best way to do that.
What's your preference? Do you prefer to know who the killer is early in the novel? Do you like to follow clues with the sleuth? Or do you prefer to match wits against the author?