Faced with evil like Lucy Letby’s, we yearn for a rational explanation. Sometimes there is none | Polly Toynbee

It is right to hold an inquiry, but the hunt for lessons to be learned' and a system to blame can easily go too far

The agony of the death of a child is something most families these days will never suffer. Through illness, accident or even negligence, that loss, and the lifelong pain it causes, is every parent's greatest fear, but to know someone murdered a defenceless infant must be beyond endurance. How could she?

We will never know what evil or insanity could have induced Lucy Letby to sweep away the lives of seven babies, and attempt the murder of another six. Everyone hearing the case of the worst serial killer of children in modern British history tries, and fails, to imagine the state of mind, the cause and how such a person grew up so apparently normal, her inner murderous impulses unobserved. Her responsibility for new lives inside the Countess of Chester hospital neonatal unit, which should be a sanctuary of the greatest safety, makes this feel like the deepest betrayal.

Polly Toynbee is a Guardian columnist

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