Crime fiction is a huge market, but it's also a market with some distinct subgroups.
When one person says they love crime fiction, they might mean they love a cozy mystery, others a gritty suspense novel. Others still might think of legal thrillers that involve a crime as being crime fiction.
Quite often, these lines are pretty permeable. There are extreme examples of both.
At one end of the spectrum, you have what I think of as 'closed' cozy mysteries. These are the 'Murder on the Orient Express' model. You take a group of suspects, and you isolate them. This could be on an island or croft, in a mansion or virtually anywhere geographically remote. This is classic crime drama - the murder is less important than the relationships between the characters. This is a 'whodunnit' in the most classic sense, and it works really well for period crime novels where DNA evidence is unavailable. It's pretty rare for there to be no trace forensics at all at a crime scene, so modern novels don't tend to use this approach as often. If they do, it's a "DNA will take x days" scenario giving the author time to use more classic techniques before affirming/ denying the investigator's current supposition.
At the opposite end, you've got your suspense novel. A serial killer is on the loose, and it's a matter of time until they strike again. The police are in hot pursuit, but are always one clue behind. This can range from a gore fest to a forensic bent to a legal bent or any combination thereof. Sometimes, you'll find authors give the readers information that the investigator doesn't have, and watch them root for the policeman/ PI/ Joe Public who gets caught up in it.
Both ends of the spectrum are great, but as authors we need to carve out a niche. Generic fiction rarely sells as well as something unusual. Unusual carries a big risk in that you either flop completely or find the target audience and excel. What makes your crime novel unique? Do you have a particularly unusual protagonist? Is your book forensically accurate? Do you know your police procedure? Can you weave in courtroom scenes?
The big crime novels tend to be in series. It's hard to create unique intellectual property, i.e. branding, in crime. The slightly flawed investigator has been done many times, and having a unique take is not easy. We've got some great regional variations - Irish and Swedish crime fiction has been doing very well for the last decade or so.
But for me, it's all about having a gripping premise. There are, quite literally, thousands of 'I shot him' novels. Nearly always, this comes back to Greed (Money, crime)/ Anger/ Jealousy (especially of the sexual kind)/ Revenge / Duress / Concealing something .e.g a crime or a family secret / Political or Religious vendettas.
This can be quite unusual e.g the duress of a kidney transplant list leading someone to bump off those above them. It's not always a neat fit within the above, but 99% of murders will fit in one or more of the above.
So, how do you write a great crime novel?
1. Firm motive - give your character a reason to care. A murdered ex, a cheating spouse, a big inheritance, their child kidnapped, etc.
2. Give them the means - and make it appropriate to the setting. Women rarely kill by violent means, so think poison rather than axe.
3. Come up with something unique in terms of premise. For example, you might pick something from forensic journals. Recently, a lab faked DNA. They took blood, and spun it in a centrifuge to remove the white blood cells. The remaining red cells had no DNA. They added DNA from saliva that had been subject to Whole Genome Amplification, and voila. Fake DNA. This is a huge problem - and would lend itself well to a court drama. You can tell when this has been done as normal DNA has a certain level of methylation that fake DNA doesn't. If your theoretical criminal was say, a scientist, and worked out how to fake that as well... then he could set up his ex/boss/ anyone who has crossed him. That makes for a compelling 'It wasn't me' story of a man or woman trying to prove their innocence against widely accepted and relied upon DNA.
So, combine all the above. Make your investigator unique - decide if they'll be a cop, a psychologist, a forensic anthropologist, a genealogist, whatever. Use ying-yang theory to make them human - a little evil in your good characters, a little good in the bad guys. Mix it up. Add something to put pressure on timelines - legal issues, kidnapped children, threat of murder/ duress. Then dump appalling circumstances on your protagonist. Every time they overcome a barrier, put a bigger one in the way. Raise the stakes, make it personal. Then break it to a great resolution in an original way.
Crime is seriously fun to write - so if you're on the fence, give it a go!
Leave questions/ thoughts/ requestions as comments - we'll try and make this a whole series for you guys. Guest posts are more than welcome - contact us in the usual way.