How could anyone do those unimaginably cruel, inhuman things?
That is the question that, to most people, immediately flows from hearing the ghastly details of both the Sheffield man who fathered nine children by raping his two daughters and, of course, the tragic story of Baby P.
We seem to have any number of inquiries and investigations now under way into trying to find what went wrong, but I wonder whether the real answer lies buried in that initial question.
The 56-year-old Sheffield businessman who raped his children and the woman and two men who tortured a baby in Haringey would all appear to fit the definition of sociopaths: individuals with a deficit or absence of the social emotions (love, shame, guilt, empathy and remorse), but with a clear facility to deceive and manipulate others.
Mr X, as the rapist was known, refused to attend court to hear his sentence but in a letter to his brother said: "I haven't got any regret over what has happened. It's too late for that. It shouldn't have happened."
Also referred to as "anti-social personality disorder", the behaviour of such people is beyond comprehension to most people because it does not equate with our understanding of what makes us human.
Academics calculate that sociopaths account for about 3-4% of the male population and less than 1% of the female population. Professor Robert Hare from the University of British Columbia is one the world's experts on sociopaths and psychopaths. He writes of people "completely lacking in conscience and in feelings for others".
He describes how "they selfishly take what they want and do as they please, violating social norms and expectations without the slightest sense of guilt or regret".
Such people are, however, very difficult to spot.
In her book The Sociopath Next Door: The Ruthless vs. the Rest of Us, American clinical psychologist Dr Martha Stout explains why she thinks this is:
Since everyone simply assumes that conscience is universal among human beings, hiding the fact that you are conscience-free is nearly effortless. You are not held back from any of your desires by guilt or shame, and you are never confronted by others for your cold-bloodedness. The ice water in your veins is so bizarre, so completely outside of their personal experience that they seldom even guess at your condition.
The individuals that society puts in the front line to try and spot the threat from sociopaths could hardly be more different. Social workers, doctors and teachers are, usually, natural carers - people who empathise easily with others. They are wired to see the best in people, to develop trust.
And most of the time, that is exactly what we want such professionals to do - to support and to help people through their difficulties. But we also demand that they retain a deep cynicism about the individuals they work with - constantly questioning and imagining the very worst.
Sometimes they must make professional judgments about people who are wired completely differently to themselves - people who do not share the basic qualities that define humanity as they understand it.
In his report [pdf] into the death of Victoria Climbie in Haringey in 2000, Lord Laming wrote of the need for "respectful uncertainty" when dealing with a child's family and of "critical evaluation" of what professionals are told. He has spoken of the "over optimism" he encountered, the way in which social workers tend to "travel with hope".
When one reads the appalling details of 25 years of abuse and suffering in the Sheffield case, it does seem incredible that it went on for so long and without anyone in authority noticing.
But perhaps it is the very incredibility that explains why.