31/01/2017 11:53 GMT | Updated 01/02/2018 05:12 GMT

What Makes A Female Murderer?

Channel 4/ Screenshot

Replete with barbed wire and buzzing magnetic gates, New Mexico Women's Correctional Facility lives up to every movie cliché. Its low-rise buildings are visible from a distance through the desert's heat haze, and by the time we pulled into the front entrance, I couldn't ignore the frisson of excitement. After the obligatory pat down and confiscation of a pen-knife, we were inside and about to film the first interview for Women Who Kill.

It had all started four months earlier when the production company I work for, Wild Pictures, began discussions with Channel 4 about a film on female murderers. To stand out from the glut of programmes on this well-trodden territory, we knew we needed at least three things: incredible stories; interviews with killers from within prison; and an editorial line that got below the lurid headlines. The question we had to ask was: 'What makes a female murderer?'

After some lengthy written exchanges, I had about a dozen confirmed interviews with female murderers in prisons across four US states: Oklahoma, New Mexico, Texas and Florida. As we looked into their stories, we saw two distinct types of killers: those who had killed as a result of a complex relationship, often with histories of domestic abuse; and those who killed for money through long processes of manipulation, the so-called Black Widows. We saw the potential for two films, one on each type of murderer.

The broadcaster wanted one of their known and trusted directors on board. They suggested Matt Pelly, a talented film-maker whose last Channel 4 film, set inside a juvenile prison in Indiana, found humanity and moral ambiguity in some very damaged and dangerous kids. He was the perfect choice.

Only two weeks after meeting each other, Matt and I boarded a plane with over 100 kilos of kit and a shooting schedule that would change by the hour! But the general plan was to film with the family and friends of each prisoner, as well as people close to the victim, before moving on to the jailhouse interview.

Our seven-week shoot was in turns shocking, moving and exhilarating. In 23 hotels and 15 flights, we experienced the mind-boggling diversity of America. One day we'd be filming with impoverished Native Americans in New Mexico, another with wealthy plastic surgeons in Oklahoma, another with a struggling single mother working 16-hour night shifts in Florida.

As we spent time with the families of these murderers, one thing was clear: their lives had appeared normal up until the point they killed someone, with no warning signs of what was to come. Unlike men, most women who kill have no history of criminality. Their crimes seemed like aberrations, moments of madness.

Yet as we dug further, it was clear these 'moments of madness' didn't happen in a vacuum. We heard about complex relationship histories, domestic abuse, alcoholism. One inmate, who had shot her husband after he abused her children, told us, 'It was like I was in prison my whole life, and I came here to be free.' Research backs up their stories. At some estimates, 80% of female murderers are victims of abuse. And of the 11% of murders in America committed by women, the vast majority know their victim as a spouse, family member or friend.

The most moving encounters were with the children of these women. They had intimations of their mothers' crimes, but no concrete knowledge. Incredibly hard lives lay ahead of them, full of stigma, guilt and confusion. Their carers - usually grandparents or close friends - had become parents again when they least expected it, in circumstances they never imagined.

By the time we got to the prisons, we had developed strong impressions of the women. To some extent, admittedly, these impressions were informed by media coverage. But as each walked into the interview room, it was hard to see the 'monster' of the sensationalist headlines. Dressed in baggy prison fatigues, often joking and smiling, they looked more like municipal cleaning staff than 'cold-blooded killers'. They were usually meek, giggly and ill at ease. Some appeared behind glass; all were watched keenly by guards. At Lowell Correctional Institution in Florida, someone gave us buzzers and said, 'Press this if you ever feel threatened.' But in all honesty, I've felt more threatened on my morning commute.

Most didn't deny their crimes; they wanted to explain them. We let them talk, listened, tried to understand. I had the impression that they, like us, were also trying to comprehend what they had done. They spoke of poor life decisions, addictions, abusive relationships, early traumas. And for most of them, when it came to the crime itself, it sounded like an inability to process long-held pain and anger had led them to snap in the moment.

The exceptions were the two 'Black Widows' featured in episode two. Confident and engaging, both denied any involvement in the murders and it was hard to break down their protective layers of denial (although Matt did a great job of challenging them). It was as if they were so adept at manipulation and deceit, they had actually deceived themselves. And it was that ability to twist reality, more than the details of what they said, that explained their crimes.

So what makes a female murderer?

To answer that, I picture those women sitting opposite us in the brightly lit interview rooms. I think of what they were in previous lives: mothers, colleagues, neighbours, friends. And I'd say that - with the exception of the rarest Black Widows - it's simply life itself that makes a female murderer. The gruelling and cruel journey that some people know as life.

Episode 2 of Women Who Kill will broadcast Wednesday 1st February, Channel 4.