Murder is, of course, an act of violence. So a good murder mystery almost has to include violence, at least to some extent. But authors vary greatly in the amount and kind of violence in their stories. Readers, too, vary in the amount and kind of violence that they like to read. It seems, though, that crime/mystery readers expect that, if there's going to be murder, there's going to be violence.
Some mystery series involve a lot of violence. That's especially true of the hardboiled detective genre such as Mickey Spillane's work. It's also true of some other, similar, series. For instance, John D. McDonald's Travis McGee series includes quite a lot of violence, and McGee prides himself on his fighting ability and physical fitness. Later in the series, some have argued that it seems McGee has become violence-weary, and that's probably true. But, especially in the earlier novels, it's an important part of the plots. Some of the Ellery Queen novels involve that kind of physical violence, too. For instance, Ten Days' Wonder begins with Howard Van Horn, a wealthy young man and friend of Queen's, waking up from a blackout covered in blood, with the realization that he must have committed some horrible crime. He asks Queen for help in figuring out what's behind his blackouts and what murder, if any, he's committed. As the plot unfolds, we see that the novel is much more than a string of violent acts, but violence permeates it.
More modern crime fiction also includes a great deal of violence. Janet Evanovich's Stephanie Plum series is one example of a series that includes violence. After all, Plum is a bounty hunter who's protected by a former member of the Special Forces. So one would expect a lot of violence. Nora Roberts, writing as J.D. Robb, has also created a violent mystery series, the In Death series, featuring Lieutenant Eve Dallas as the sleuth in a futuristic setting.
Of course, not all murder mysteries focus as much on the violence of murder. Laurien Berenson's Melanie Travis series is one example. In this series, Berenson certainly describes how the victim is killed, and her sleuth, Melanie Travis, gets into more than one dangerous situation and is hurt a few times. However, the violence isn't graphic. It's not graphic in Dicey Deere's Torrey Tunet series, either, nor in Rita Mae Brown's Mrs. Murphy series.
For the author, there is always a balance to strike when it comes to violence. Many people's taste runs to violence, so there's a temptation to include it, so as to keep readers engaged. In fact, Agatha Christie discusses this very point in The Clocks and, even more directly, in Hallowe'en Party . In Hallowe'en Party, Christie's fictional mystery author, Ariadne Oliver, is helping prepare a house for a Hallowe'en party. When one of the guests, a young teeenager, finds out that Oliver writes murder mysteries, she claims to love mysteries with "lots of blood." In Cards on the Table, Oliver tells Rita Dawes, a fan of her work, that she sometimes has to include another murder and, "get the heroine kidnapped again," if her novel isn't long enough or interesting enough to satisfy her editor.
Yet, Christie herself doesn't include gratuitous violence. In fact, Hercule Poirot may very well be the voice for Christie's view about violence. As a former member of the Belgian police force, he's seen a lot of violence and gore. It bores him. We see that in Murder After Hours (AKA The Hollow). In that novel, Poirot is invited to lunch at the home of Sir Henry and Lady Lucy Angkatell. When he arrives, he sees the body of Dr. John Christow, who's apparently just been shot, lying beside the pool. At first Poirot thinks it's a scene staged for his benefit and the thought of that makes him weary and annoyed. It's only after he finds that the crime is real and involves much more than the violent scene he's witnessed that he gets interested in the case.
My own Joel Williams series doesn't include a lot of graphic violence. It's not that I'm squeamish; I'm not. It's more that I think the intellectual challenge of solving the mystery is a lot more interesting than gore is. Also, I must confess, I don't enjoy writing graphically violent scenes, so I don't write them as well as I do other things. Other authors do things differently.
What's your view? Do you avoid violent series? Prefer them? Does the amount of violence make a difference for you?