"Our worlds were shattered when we encountered evil disguised as a caring nurse." That was the heartbreaking comment of one parent who lost a child to Lucy Letby, the nurse who murdered seven newborns and may have harmed up to 30 more.¹

There is one detail that has stuck in the mind of the parents of so many of the victims. As she tended to the tiny, broken bodies whose lives she had taken, she often seemed oddly cheerful- even happy.

Yesterday she was sentenced to a whole-life prison sentence. But her trial left one question unanswered: why did this ordinary woman, with an ordinary upbringing, commit such horrifying crimes?

It has left many reflecting on the nature of evil. Some suggest that she is an example of what philosopher Hannah ArendtA Jewish German political philosopher who escaped a concentration camp and fled to America. She wrote extensively about Nazism. called "the banality of evil".

Arendt was talking about Adolf EichmannThe senior Nazi in charge of organising the deportation of Jews to extermination camps during World War Two. He was convicted of crimes against humanity and hanged in 1961., one of the most important organisers of the Holocaust. Arendt argued that Eichmann seemed ordinary, even dull - certainly far from evil. But it was his dullness that allowed him to do such evil things. It meant he just did whatever he was told.

Letby was the same: someone who seemed entirely average, and so would never have been suspected of killing the most vulnerable people under her care.

But others say evil is not just in what we do: it is in who we are. American thinker Judith ShklarA 20th Century American philosopher and political theorist. suggested that the most important moral value is the rejection of cruelty.

The picture painted of Letby in her trial is one that reeks of cruelty. The court heard that she used to spend hours looking at the Facebook profiles of her victims' parents, drinking in their grief. Shklar thought we should recognise this taste for cruelty as the true form of evil.

Yes: Letby does not seem evil. She was not overflowing with hatred and bile. There have been suggestions she was trying to impress a doctor she was in love with. She was an ordinary person who did terrible things. 

No: What we find horrifying about Letby is her cruelty. She still seems to feel nothing about the babies she killed or the families whose lives she broke. In that cruelty, we see the very depths of evil.

Or... Whether or not Letby is evil, it is important not to become too disillusioned and start seeing evil everywhere in human beings. Most people are neither unusually cruel nor entirely evil.