CPS admits it made mistakes with Lucy Letby evidence: Door swipe data 'vital' to showing which nurses could have been on the ward was incorrect

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Evidence used in the trial of Lucy Letby showing which staff came in and out of a baby unit was incorrect, the Crown Prosecution Service has admitted.

The killer nurse was last year found guilty of murdering seven babies and attempting to murder six others at the Countess of Chester Hospital.

A jury at a retrial last month convicted Letby of the attempted murder of another child – known as Baby K. 

But prosecutor Nick Johnson told the court during her retrial that data showing which nurses and doctors swiped into and out of the intensive care ward had been 'mislabelled'.

During the first trial, the prosecution said consultant nurse Dr Ravi Jayaram had found Letby standing over the deteriorating Baby K at 3.50am on February 17, 2016, and that its breathing tube had been dislodged.

The prosecution argued the door-swipe data showed that Baby K's designated nurse vacated the intensive care unit at 3.47am. 

However, the amended data in the retrial showed the nurse had returned at that time, so Letby cannot have been alone.

In both trials, door-swipe data was used to show that Letby was the only nurse present in the unit when babies rapidly deteriorated.

Although the discrepancy was discovered and corrected for the retrial, Conservative MP Sir David Davis has written to the chief crown prosecutor of Mersey-Cheshire CPS demanding clarification, the Telegraph reported last night. 

He said: 'It is essential the CPS makes it plain whether those errors occurred throughout any of the evidence of the first trial.'

The validity of Letby's initial trial has recently come under scrutiny as several scientists second-guessed the medical evidence heard by the jury.

During the initial trial, the prosecution argued that Letby was 'a constant malevolent presence' when babies became ill or died at the Countess of Chester Hospital.

They used door swipe data to show that Letby was the only nurse present when Baby O first collapsed.

The prosecution said that 'within a few minutes of Lucy Letby coming back on the neonatal unit, as shown by the door entry swipe system, [the baby] suffered his first collapse'.

In a separate incident, Baby A's collapse was found to be consistent with a deliberate injection of air when only Letby was in the room.

A spokesman for the Mersey-Cheshire Crown Prosecution Service said: 'The CPS can confirm that accurate door swipe data was presented in the retrial.'

Letby received a whole life sentence and will die in prison as a result of her crimes. 

Sir David is currently analysing the evidence used to convict the neonatal nurse.

The former Brexit secretary launched his investigation after doubts were raised about Letby's guilt - with some members of the Royal Statistical Society expressing concerns over the use of statistics to secure a conviction on the basis of probabilities.

Mr Davis, a civil liberties campaigner, is understood to be concerned about the justice system's institutional reluctance to admit to its own failings, leading innocent people to languish in prison.

Last week he told The Daily T Podcast that he would visit Letby in prison if he was 'at least three-quarters persuaded that she's innocent'.

He said: 'I may not be allowed to, her lawyer may say no; she may say no. That's got to be with her permission.

'For me to do anything about this, I've got to be at least three-quarters persuaded that she's innocent.

'I'll read millions of words of evidence over August and come to a conclusion in probably September or maybe October.'

Mr Davis has said that if after speaking to experts, he does come to the conclusion that she is innocent he will raise the case with parliament and seek to get a Criminal Case Review Commission referral.