By Professor Philip Stenning
I have a suspicion that Mark Featherstone's (and perhaps Levinas') underlying assumption (that a parent "naturally" puts his or her child first) may be incorrect. In the animal world, parental killing of offspring at or soon after birth is not uncommon. So if such protection of offspring is not "natural" for animals, it's not easy to see why it should necessarily be "natural" for humans. And of course, we know that infanticide (defined in law as the killing of a child by its mother who is lactating) is not uncommon among humans. It is also an established fact that those who are at greatest risk of homicide are children under 5 years of age, and that parents or step-parents are frequently the perpetrators.
Of course, if we assume that "putting one's child first" is "natural" (rather than just normal) human behaviour, any parent who kills or inflicts such extreme violence on their child must by definition be acting "unnaturally", and this allows us to characterise them as "not human" or as a "monster" or "devil", and to conclude (as you seem to) that such killing is not humanly understandable or explicable.
But if we resist this kind of thinking, and accept that killing of one's child is not "unnatural" in this sense, trying to understand or explain such a killing becomes a matter of trying to understand /explain why the parent has departed from such an established social/ethical norm. This opens up all kinds of possible explanations, such as extreme intoxication, mental illness, delusion or hallucination (there's a famous English case in which a father put his baby on the fire under the delusion that it was a log), supposed divine instruction (there have been many cases - and not just in the Old Testament - in which parents have claimed that God told them to kill their children), or some failure of socialisation against violence (e.g. if the parent was a victim of such extreme violence as a child).
Of course, every right-minded person will be horrified by the circumstances of Baby P's death, and no decent person could accept or excuse the prolonged torture and killing of such a helpless baby. But I think that characterising such behaviour as "unnatural" may not be helpful as far as seeking possible explanations for it, which may in turn help us to prevent similar cases from occurring in the future.