SINCE the beginning of time, myths and fairy tales of maternal filicide (the killing by a mother of her own child) have been embedded in literary and folkloric culture across the globe. One of the earliest and most famous is probably the Greek myth of Medea, wife of Jason (of the Argonauts fame) who, in an act of revenge following Jason’s affair with another princess, killed their two young sons. In contemporary diagnostic terms, this is known as "revenge filicide". There are others, such as Hansel and Gretl and Snow White, whose wicked parents or step-parents attempted to kill them by luring them deep into the forest.

The murder of innocents and innocence is as old as time. It was not until the fourth century AD that the killing of a child was made illegal when Emperor Constantine (a convert to Christianity) introduced a law making infanticide punishable by death. This was in distinct contrast to the ancient Roman law "Pater Potestas", which deemed that a child's father had a legal and moral right to decide whether the infant should be allowed to live after birth. From the Middle Ages until the end of the 18th century, infanticide was the most common crime in Western Europe as a result of high rates of illegitimacy and economic austerity.

Women kill their children for many reasons. The cause may be altruistic, where they believe the killing is in the child’s best interests because of illness, disability, deprivation or real or perceived threat. In these cases, the mother’s judgment is often impaired by serious mental illness and social isolation (she may be psychotically depressed and suicidal and feels she cannot leave the child to live in a cold, uncaring and motherless world).

There are mothers who kill because their child is unwanted, an inconvenience. In these scenarios, mothers often seek to gain benefit from the child’s death through insurance, inheritance or because they want to be free to marry a partner who refuses to carry the baggage of someone else’s children. Another category is "accidental filicide", where a mother unintentionally kills her child as a result of extreme rage, abuse or neglect. An example of this is Munchausen Syndrome by Proxy, where the mother’s pathological need for attention results in the deliberate injury or even killing of her own child, enabling her to get the attention she craves by seeking medical intervention. Last year, Lacey Spears was jailed for 20 years in the USA for the killing of her five-year-old son, Garnett, by poisoning him with salt over a five-year period. She chronicled her son’s "illness" throughout the course of his short life in a blog called Garnett’s Journey.

It is hard to grasp the level of mental and emotional splitting required in a personality to enable such gross acts. Needless to say, Spears would have prioritised her own needs for attention over those of her son’s right to life. In this sense, she would have been profoundly and dangerously narcissistic.

The murder of two year-old Liam Fee by his mother, Rachel Fee (32) and her wife, Nyomi Fee (28) is so horrific that most of us reach mental and emotional impasse when confronted with the details of the case. Our imaginations struggle to wander into the dark hinterland of brutality and sadism that was the home Liam knew. His post-mortem revealed that he died of a ruptured heart due to blunt-force trauma to his chest and abdomen. He had 30 external injuries, a broken thigh and a broken arm. Both these fractures happened days before his death and Liam would have been in agonising pain as a result.

Why did his mother and her partner inflict this upon him? Why wouldn’t or couldn’t they provide the love and care Liam needed and deserved? And, just as disturbing, why did they then try to frame one of the other young boys in their care and whom they had also subjected to extreme physical and psychological abuse?

In all likelihood, we will never get to know how these two women thought or felt about themselves, about their child, about others. It is possible that they themselves will never understand why they murdered Liam or worse, they may not be interested to inquire within. They may be so disordered and damaged in personality that they are incapable of reflection and remorse. Much more likely is that for the foreseeable future, both women will continue to deny their actions and blame others. Throughout the history of this case, both women lied consistently about the origins of Liam’s injuries. They felt victimised when social services suggested that Liam’s injuries were not accidental and that he was suffering from neglect. They closed ranks and were paranoid and manipulative in attempting to hide their abuse of Liam and other children in their care. Details of some aspects of the abuse are so depraved and disturbing that they could not be reported outside of court.

Their "folie a deux" must, in part, have been a factor in Liam’s murder where their co-dependency intensified and exaggerated their cruelty rather than mitigated it. Ian Brady and Myra Hindley are notorious examples of this, as are Fred and Rose West, Bonnie and Clyde. In such lethal pairings, one plus one create a world that, although distorted and depraved, becomes normalised, rational, justified. The only reality-check they know is their own desire, their own sense of engorged entitlement. Others, even their own children, are simply objects on a stage that they manipulate at will in order to set the scene directed by their profoundly disturbed personalities.

Rachel and Nyomi Fee were, in this sense, collaborators and co-directors. It was them against a cruel and persecuting world where everyone was out to get them and where they had to be on the lookout constantly for hostile attacks by social services, childminders, doctors and the police. Many of their Google searches in the days and weeks before Liam died indicate just such a mindset when they inquired: “Do I have to see a certain doctor?”; “How long can you live with a broken leg” and – “Can social services gain access to my house?” Then, chillingly, towards the end: “Can wives be in prison together?”

Given the Fees’ level of deviance in executing and covering up their crimes, their stupidity in using internet searches is striking. Yet, in some ways, this is fitting with their world view, a grossly diminished and grotesque cosmos in which the only reality is the one they share together, a world where nothing extends beyond the boundary of gratifying their own needs.

Everyone and everything outside of this is an obstacle, a foreign body in the ointment of their "malignant narcissism". This term is used to describe a cluster of personality characteristics, including extreme narcissism, anti-social personality disorder, aggression and sadism. Malignant narcissists are often pathological liars, capable of dehumanising the people around them, particularly those they perceive as weak and vulnerable. They serve their own interests above all else and are usually incapable of feeling remorse. In this respect, they are also psychopathic and, therefore, dangerous. They are not "mad" in the sense that they are psychotic and out of touch with reality. It is more that they construct a reality that is devoid of the qualities that we associate with being humane, compassionate and moral, and thus create an internal world that has no conscience, no moral or emotional compass to keep them in check.

No doubt, psychological reports will reveal some elements of malignant narcissism in both Rachel and Nyomi Fee. Their own childhood backgrounds may well include experience of emotional deprivation and possibly trauma as a result of violence or domestic abuse. It is highly unlikely that these women came from secure, loving families where they felt valued and cared for. Whatever the circumstances of their upbringing, it resulted in two disturbed individuals pairing up and acting out their own grievances onto a totally helpless and dependent toddler. Sadly for Liam, neither woman was able to give him the love and care he needed in order to survive because both these women, paradoxically, probably felt deprived and unloved themselves as children. In killing Liam, they killed off the vulnerable child within themselves. Perverse and tragic.

Photographs of Liam Fee have been in the media over the last seven weeks of the trial. I was struck by the liveliness of his expression, his eyes fully engaged and connected with the person taking the picture (possibly his mother Rachel Fee). He seems happy in the moment. I wondered if, in fact, his happiness stemmed from the fact that for a brief moment in time, he feels loved, attended to, safe. Just for a second, things seem normal. There is possibility in his open eyes, a real potential for something better. Rachel and Nyomi Fee diagnosed Liam as being "autistic" and having learning difficulties. One wonders if this was a smokescreen to divert attention from the fact that Liam’s own internal world must have been horrifically and terrifyingly confused. He would not have been able to trust the adults around him. He would have struggled immensely to try and make sense of the world he found himself in. His life would have been tortuous and profoundly unhappy. The inquiry into his death will examine how Liam was failed. Failed, not only by Rachel and Nyomi Fee, but by all of us, by society itself. Too often, as adults, remote from our childhood selves, we lose touch with the wonder and innocence of childhood and forget how profoundly vulnerable and dependant we were on those around us to keep us alive, to show us how to be persons capable of giving and receiving love. If we could turn back the clock, I'm sure all of us would have wanted to make things better for Liam. One of the other children in the Fee household, when being interviewed by police and social workers after Liam's death, was asked about his keen interest in superheroes, specifically Batman. He said he loved comics because "the good guys always win". Is it too much to hope that all of us, including those in authority and responsible for leading the way in child wellbeing and education, can make this little boy’s superhero dream more of a reality?

Sadly for Liam Fee, he died too soon and it is now too late. His death, whether we know it or not, is a profound loss for all of us.