It is an illusion that most women are far removed from being able to commit these sort of savage acts. For the majority of men and women, it is guilt and remorse that gets in the way of killing.

The difficulty is to understand how and why people, especially women, commit these sorts of crimes when the usual societal rules are still in place.

The important thing to realise is that there is such a genetic variety among people that there will always be psychotics and sociopaths. Women are just as likely to be miswired in this way as men but they have the extra restraining factor of cultural female norms and genetics, which make them more aware of the consquences of their actions, both for themselves and their victims. Men's wiring is simpler: it's relatively easy to train a man to be a mindless killer, as we have seen repeatedly and frequently over the centuries.

The issue of why women abuse children and other women is such an emotional one that what people often fail to recognise is that there are more differences within the sexes than there are between them. Women can be just as aggressive and cruel as men, given the specific set of circumstances that brings forth that behaviour.

What tends to be true is that even if a woman has the capacity for atrocities inside her, the catalyst to bring those behaviours to the surface often seems to be the presence of a man who lacks the imagination to empathise with his victims or restrain his desire for power and sexual or violent gratification. Women who abuse are less unusual than we might like to think. Men tend to be the more common abusers, especially of children, but when a woman does do it, they often do it horribly. Often it seems to be about anger rather than sexual or power gratification. The anger could be due to her resentment that her charismatic man, as she sees him, wants someone else.

This puts her in a dilemma: either she helps him procure the victim, or she risks losing her lover.

Once the victim has been obtained, it could be that she copes by blaming them for tempting her man and takes out her revenge by colluding in their physical and mental torture. Becoming active in the torture also protects against the risk of a power shift, where the man ends up more interested in the victim than in his wife or partner.

The other theory is that it's pretty thrilling and exciting for someone with catastrophically low self-esteem or low intelligence to be chosen by a man who recognises no superior authority but exhibits pure Nietzschean free will. There can be a horrible Faustian pact based on what therapists call "splitting and projecting": the fact that she worships this special man and subsumes herself to him, gives her – perversely and additionally – status and position. But this reflected glory only exists in relation to him. If she leaves him – or he leaves her because she ceases to please him – she loses that status and ends up even lower than before.

To be trapped in the centre of a great secret with a man perceived to be so charismatic can also be hugely exciting. There is something thrilling, compelling and obsessive about the idea. Added to that is the fact that it's just the two of you against the world. You have both burned your bridges and are outlaws together.

The truth, however, is that you can't have a theory that covers all the reasons why women can commit these sorts of atrocities. There is no satisfactory explanation that can be neatly packaged. Some women have a very poor mental grasp and are swayed by primitive and horrible beliefs.

Some people are, in the old-fashioned lingo, evil.

Phillip Hodson, fellow British Association for Counselling and Psychotherapy