In British author Alex Marwood’s The Killer Next Door, body parts start surfacing in a seedy London boarding house.

What draws you to write about crime?

I’m fascinated by the human condition in its extremes. That is when we find out who we are and what makes us work. I’m interested in crime from all angles—the effect on both the victim and the perpetrator; the incompetence, bad decision-making, and sins of omission that often lead to terrible consequences; and the strange allegiances that can grow through these experiences. But mainly I just have a dark bit to my soul.

Are any of your characters modeled after people you have known?

Like most writers, I’m a magpie for other people’s character traits. In The Killer Next Door, Vesta Collins, one of the tenants of the boarding house, is closely based on a friend who died a few years ago. Unlike the childless Vesta, [my friend] did have a child, who was a nasty piece of work, and in the end she had quite a lonely death.

Is the murder of the child the two girls, Kirsty and Amber, commit in your previous crime thriller, Wicked Girls, based on an actual crime?

I’m fascinated by the difference between court reports and the unrecognizable stories they become in the media. While writing Wicked Girls, there was a terrible case: Christopher Jefferies underwent a brutal trial by media when his tenant was murdered. Everything about the man—his enthusiasms, his eccentricity, his unorthodox haircut—was twisted shamefully by the media, suggesting open-and-shut guilt when he had nothing to do with the girl’s death. It made my blood run cold and fed into the experiences of Kirsty and Amber.

Did you plot the unexpected endings of The Killer Next Door and Wicked Girls before you started writing each book?

I always start off meaning to be a plotter, but in the end something else—some weird hypnotic influence from the characters themselves—will take over and lead me way off my intended path. The resolutions of all my books have come to me late in the day. I wish it were otherwise, because it makes the writing process horribly stressful

In both books, characters’ lives are ruined by events beyond their control. Do you think this mirrors life?

Yes. Those who believe they can avoid random misfortune, or believe that having done so reflects on their own character, are kidding themselves. Nothing is more interesting than examining how people cope with the random bad luck that could hit any of us.