You sit alone in front of a computer and you think about how you want to kill someone. The technical details, they’re easy enough. The time and the place, the weapon of choice. You’ll have a victim in mind and a reason to do it. Then, when the moment comes, you need to be inside the head of someone hopefully most unlike you. You have to think like a killer.
There are, obviously, different reasons why people kill, and each one brings its own challenge. Trying to think like someone in such a state that they would lash out unthinkingly and commit murder is not easy to do. Most of us will never be so enraged, so disturbed, that taking someone else’s life would seem like a good idea, not even for an uncontrolled split-second. What drives a person there? We put people through the wringer in crime novels, push them until they crack, and when they do, they have to seem convincing. That’s when your head has to be in a similar place to theirs.

In some senses it’s a leap of faith. You probably can’t accurately reproduce the mind-set of a violent offender by sitting at a computer and taking a guess, but you can get as close as possible. What thought process leads to the moment of attack? In many cases it has to happen quickly, unplanned and rushed, frantic movements and a clouded mind. These things are hard to understand, difficult to replicate, but close your eyes and imagine the worst and it’s almost possible.
My books have tended to focus on people who kill for a different reason - money. That takes a very different sort of person again. Where the spur of the moment killer is driver by emotion, the hitman must avoid that very thing. The last thing he needs is to have emotion get in the way of a well-planned kill. He dehumanises the target, reduces them to little more than a technical challenge, and carries out every element of the job with what he hopes will be robotic precision. That absence of feeling is inhuman. The hardest part of writing about such a person is trying to recreate the disconnect, finding a way to speak about the victim as though they’re objects of no true value.

Once you get past that hurdle, you then have the challenge of writing the killer when they’re not at work. How normal can such a person be? Logic suggests that if they exist and they’re able to avoid capture then they must be able to convince those around them that they are within the realms of normality. Odd, perhaps, but not a person of concern. We like to think we would spot them, the dull look in the eye, the lack of heart, but that makes a false assumption. A person skilled enough to plan and carry out the job successfully would surely also be intelligent enough to realise the need for an act, to pretend that they were someone else. Mr Normal. Mr Decent. Smart and alert as we fancy ourselves, the chances are they could waltz through our lives without us noticing. So write them normal, capable of great deception.
That may be the hardest thing of all. Writing a killer as a normal person. Hold back the desire to make them openly evil because if it was out in the open they would be spotted on page one. The act of killing may be exceptional, but the person carrying it out may not. So with all that done, you switch the computer off and you step away from your murder. Clear your head and get back to normal. Well, as normal as possible.

Malcolm Mackay's novel, Every Night I Dream of Hell, is out now.