Some crime fiction has genteel characters, plots that are mostly puzzles, solutions that are arrived at with dialogue, not guns. Any violence mostly takes place "off stage." Think Agatha Christie's Hercule Poirot. Or Rex Stout's Nero Wolfe. The crimes can often be violent - murder, for example - but we don't witness the violence. We just see the aftermath. The solution is more a mental exercise than a physical one.
On the other end of the spectrum are stories like Lee Child's Jack Reacher books. The violence simmers throughout, serious, nasty violence that often boils over. The resolution of the Reacher stories is mostly violent. Reacher rights the wrongs of the bad guys by bringing serious violence to them, breaking bones and often killing them as well. The body count can get very high. Sometimes I think Child took as a model Shakespeare's tragedies, where nearly everyone dies at the end, onstage.
Regardless of the writer's approach, many people read crime fiction because it usually provides justice at the end. This is unlike the real world, where justice is often absent or unsatisfying in some basic way.
A writer doesn't need to have violence to tell a good story. But a writer does need a balance between the violence perpetrated by the bad guys and the violence enacted by the hero during the resolution. If the crime is presented as a puzzle, then we expect the solution to be largely mental, a thought process that solves the puzzle and delivers the bad guy to the legal system. Those stories may have little or no violence.
If, instead, like Shakespeare, the violence takes place before our eyes, we come to expect that the resolution of the story will have violence. To be satisfying, those components need some balance.
We recently rented a multi-episode show on Netflix that was well-written, smart, had interesting characters, and a good backstory. (I won't say the name of the show for the same reason I don't write one-star reviews. Nothing is gained by it.)
But it was unsatisfying because this violence equation was off. The show depicted horrific crimes involving the trafficking and selling of young women. There was also murder and torture. It wasn't a blood bath, and the worst of the crimes took place offstage. In this regard it was like so many crime shows. Not a gorefest, but a realistic depiction of crimes that happen every day.
As the show went on, we "knew" that the resolution would have a kind of emotional payback. Not only would the bad guy get caught, but there would be at least some violence directed at that bad guy. Like most viewers, we didn't want the bad guy to be tortured for his crimes. But we wanted to see him make a run for it, and in the process see him experience at least some kind of pain or physical injury, a taste of what he's done to his victims.
Unfortunately, after 90 minutes of watching the good guy trying to catch the horrific criminal, the resolution was seeing them put handcuffs on the bad guy. Nothing more. The bad guy who'd caused so much terrible suffering suffered nothing.
This left us feeling disappointed and even a little cheated. The writer/director apparently thought that despite a story about violent crime, having no violence happen to the bad guy at the end would satisfy sophisticated viewers who are "above" prosaic shows that depict violence. The show was probably realistic. But unsatisfying. And it's my guess that this approach is why this otherwise smart show was canceled after two seasons.
We writers need to remember the lessons of Shakespeare. If you want to satisfy readers and viewers, you need to give them at least a little bit of payback and bring some bring pain to the bad guy who caused so much pain.
The scales of justice in the world of fiction need to have more balance than those in the real world.