Last week’s sentencing of serial killer Joanna Dennehy, for the murder of three men and attempted murder of two others, reminded me of the extreme dangerousness of psychopaths such as Dennehy, and why a life prison sentence is the only appropriate punishment. In the US, 19 year-old Miranda Barbour has confessed killing at least 22 men whom she met for sex through a Craigslist website. Predictably,the press has been awash with articles attempting to understand such crimes, agonising over how such horrors could ever have been carried out by a woman.

Sadly, I don’t see these cases as inexplicable or unique. While researching my book on female violence and aggression, Deadlier Than the Male, in the 1990s, I interviewed one of the UK’s leading forensic psychiatrists, Dr Jeremy Coid. He left me in no doubt as to the horrifically complex and mostly incurable behaviour of women who get their thrills from torturing and killing. Dennehy’s and Barbour’s lack of remorse and self-confessed enjoyment of the act of murder are all of a piece with Coid’s definitions of what lies behind such actions.

Coid, who has interviewed almost 100 women in maximum security hospitals including Broadmoor and Rampton, discovered that many derived extreme sexual arousal from thinking about acts of torture and killing, planning those attacks and then carrying them out. A large erotic aspect of such behaviour is fantasy – as it is with many male serial killers. In these women’s fantasies, whether they imagine themselves killing men or women, they invariably imagine themselves as the dominant sexual partner. Their sexual fantasies, as well as their behaviour in everyday life, is invariably highly aggressive, predatory and promiscuous and involves victims, male or female, who are essentially submissive and unassertive. The women he talked to confessed to being turned on by sex games, real or imaginary, which included sado-masochism, physical violence and rape – with an appropriate weapon. According to Jeremy Coid, the women he interviewed described the peak of their sexual fantasies as the murder of their partner during orgasm. Such masturbatory rituals became increasingly elaborate, well rehearsed, and repetitive.The women reported that desire for a penis to be able to “rape like a man” was part of the excitement of violence. Like male serial killers, the women became addicted to violence and sadism, sometimes from their early teens on.

Just as disturbing were some women’s lifelong obsession with decapitation, arson, knives, and other instruments of death. In very extreme cases, they fantasised about raping and killing old or disabled people, animals, even children. We may think such fantasies, albeit revolting, are in themselves harmless, as long as they always remain fantasies. But they don’t. The pattern of acting out imaginary scenarios seems no different for violent psychopathic women than it is for male serial murderers, whose diaries, videos, drawings, and stories of sado-masochism offer as much insight into their hideous inner landscape as the crimes themselves.

So it is for violent women. The more sexually arousing a woman’s sexual fantasy, and the greater the fulfilment derived from imagined acts of sadism, domination and murder, the more frequently she is likely to indulge those fantasies, until the ultimate gratification: planning and carrying them out for real. Some Women convicted of crimes of sadism and violence admitted to Jeremy Coid that they may not have always experienced sexual thrills while planning and committing those acts, but that the accompanying adrenalin rush and subsequent exhaustion following an attack was the only way they could relieve the persistent tension and anger that had troubled them all their lives. The discovery that women may act violently to dispel their almost unbearably stressful feelings is one of the keys to understanding why women kill – and enjoy it. The chilling truth is that this is very similar, if not identical, to men who kill.

That’s what makes the fate, like the actions, of Joanna Dennehy and Miranda Barbour so tragic.