I shook hands with a murderer once. I didn’t release it at the time.

I was a new reporter working on my first, big missing persons story and had been granted an unexpected interview with the family of a teenager who hadn’t returned home for three weeks. She was out there somewhere, texting her mother from time to time, saying she was ok but didn’t want to come home. So I jumped in my car to try and find the small village in the middle of nowhere in the South Wales valleys. I’d been ordered to come back with something interesting before the late deadline, a nice colour piece for the next day, an appeal from the anxious mum and her partner.

It was a strange experience, sitting in the neat front room of the small terraced house while a white-suited forensic officer made a show of dusting fingerprint powder on a stack of CDs and books. The mum was clearly upset, her boyfriend tongue-tied, finding it hard to answer my simple questions about when he’d seen the girl last, what he’d tell her if he could appeal to her directly. I was in ‘reporter mode’, not allowing myself to think about what they were going through, trying to be gentle and sympathetic but all the while struggling to get something worthwhile from the interview, some usable quotes. I had one eye on the clock, thinking of my deadline approaching. I knew I’d have to be a bit creative to please my editor so I hared back to Cardiff with a bundle of scribbled notes and we ran a simple story.

A week later two CID officers turned up to interview me, the tables turned for once, seizing my notebooks with the scribbles inside. Some weeks later they arrested the man for murder and many months later he was convicted of killing the teenager, lashing out in a fit of anger then hiding her body in panic. The worst thing was that he appeared to have been sending texts from the girl’s phone for weeks aftwerwards, to make people think she was still alive. The police must have suspected all along. They’d probably approved the interview because they’d wanted to see how he’d react to my questioning.

I told myself that I’d known something wasn’t right, that I’d suspected, but had I? He couldn’t meet my eye but I’d put his nerves down to nothing more than the fact that no one likes to speak to a reporter. The missing girl had died in that house, where I’d shook the parents’ hands when I left. It alarmed me to think I’d been sitting five feet from someone who could do something like that, that I’d been oblivious to the fact I was at the scene of something so terrible.

It was the first of many experiences that made me realise how ordinary people can hide awful things. It was the first time I really thought about writing a crime novel because that simple fact interested me more than tales about complicated serial killers and their elaborate plans. The truth is terrible enough. The simplest choices have dreadful consequences – ordinary people are capable of horrifying acts.

The mystery is that we don’t find more people hiding horrifying secrets, or perhaps that we never suspect them…