“My parents are Viennese Jews, so my father had to leave when he was very young, and my mother lived as a teenager under Nazi rule for three years. I grew up wondering about horror and cruelty and how apparently good people can do such evil things.” Anna Motz is explaining what drew her to studying how, why and where women are violent.

She’s worked in the field for 25 years, the last 12 spent in forensic services in Oxford, working primarily with female offenders. “I wanted to understand extreme acts of violence, particularly in people who seem quite ordinary – that contradiction seemed so interesting to me.”

Her job has brought her into contact with women who harm themselves as well as others, including their own children, sometimes fatally. Her book The Psychology of Female Violence is now a standard text for clinicians. In it she writes about the nature and causes of female offending, covering sexual and physical abuse of children, infanticide, fabricated and induced illnesses, and self-harm.

She was drawn to work in institutional settings and with deprived populations. “I saw that people who had committed acts of violence that were really quite difficult to bear or understand were often repeating acts that had been perpetrated against them,” she says. “I was fascinated to understand the victim inside the perpetrator.”

She became particularly interested in women offenders when she noticed that, as perpetrators, they presented quite differently to men – gentle and meek, on the face of it at least. “Some were psychotic and that was easier to understand,” Motz says, “but meeting women who had been cruel for other motives was particularly interesting and disturbing in equal measure.”

I believed her murderousness had permeated into my own uterus and killed my baby.

Psychiatrist and psychotherapist Dr Estela Welldon mentored her, and the two remain close friends and colleagues. “When I first learned her model for understanding female perversion,” says Motz, “[it] fitted perfectly with the women I had already encountered in prisons, secure hospitals and in the community – mothers who had killed or hurt their own offspring and themselves.”

But what effect does this kind of work have on a person? “I felt very disturbed by some of the mothers,” Motz says, adding that, at times of vulnerability in her own life, some cases nearly overwhelmed her. “There was one, about my own age, who killed her child in a terrible state of unwellness and false belief. I worked with her and became so distressed in my own pregnancy that I believed her murderousness had permeated into my own uterus and killed my baby.”

The dividing line between ‘us’ (sane people) and offenders is more blurred than most of us would like to admit. “I felt I became psychotic in that session,” says Motz.

“Generally one can have these brief ideas, on the subway, say, ‘What if I jumped?’, or ‘What if I strangled my daughter?’ It is frightening… but I am sane, I have support,” she says. “But something could trigger and upset those carefully constructed defences and I could do something irrevocable and tragic.

“The work can take hold in your mind, especially if you are trying to understand,” she says. “It can send you a little bit mad.”

Her latest book, Toxic Couples: The psychology of domestic violence, examines and develops Welldon’s theory of ‘malignant bonding’ between couples and how children are used in toxic relationships.

One chapter is on Motz’s encounter with homeless girls, something she describes as “bleak reading”. She describes girls who run away from the care system and end up on the street, where they are “pimped or get into hard drugs, and are misused or trafficked”. Often, a girl gets into a violent relationship with someone they feel is their soulmate, but who is also deprived or neglected. “They have a baby, and then the baby gets removed and there is grief and loss,” Motz says. “There is the desperate wish to have a baby and a home, and it is tragic that these needs don’t get met.”

Motz has left the frontline now to work in consultancy and training. “Forensics is urgent and exciting, but it’s a young man’s game,” she says. “It can be quite macho, with gallows humour in the canteen, or a sense of Florence Nightingale in women.

“I’m glad I’ve done it,” she adds, “But you get into this distorted world where only serious abuse counts. All suffering counts.”