Lucy Letby: Questions grow in debate on killer’s convictions

“It was only the fact that I got authoritative calls from people who really know about statistics, about medicine, about science, about law, and I’d never had anything like this happen before,” he said

“I started to think – it’s a terrible crime, but if they’ve got it wrong, it’s a terrible miscarriage of justice.”

Sir David said he believed other possibilities for the deaths could have included a lack of staffing and training on the unit and an infectious outbreak, possibly linked to the faulty drainage discussed in the trial.

“All of us find it easier to believe that a villain has killed people rather than a system or a random act,” he said.

He is now reading through thousands of documents detailing the trial before making a decision on whether to take the case up and press for the Criminal Cases Review Commission to get involved.

Sir David said he already believes that the trial was flawed but by itself that does not mean Letby is not guilty.

He added that he will not take it further unless he comes to the conclusion that she was probably innocent.

Some of the parents of the babies who died have spoken of their pain at seeing doubts being raised on the convictions.

Sir David said he does think about this and understands that they have gone through years of suffering.

But he said if the conviction is proved to be unsafe, it is important to look at other reasons which may have led to what happened.

“If we have got this wrong it’s not just that we’ve put a young woman in prison for the rest of her life effectively, it is also that we haven’t answered by these babies died, and why other babies may die,” he said.

But others question the basis for claims that the trial was flawed.

Barrister Tim Owen KC has spent 40 years as a defence lawyer, and worked on many cases which he successfully referred back to the Court of Appeal and the Criminal Cases Review Commission.

He also co-hosts a legal podcast, Double Jeopardy, which has examined the Letby debate.

Much has been made of the fact that the Letby case relied on circumstantial evidence and no-one definitively saw her harming any of the babies.

Mr Owen said this point is far less relevant than many might think.

“Some people believe that circumstantial evidence isn’t really evidence,” he said.

“That’s simply not true.

“A circumstantial case can be a powerful case but in order to understand it, you have to look at the totality.

“You can’t just pick one little bit and say, ‘Oh look at that, that’s unreliable,’ or ‘That doesn’t prove anything’.”