Lucy Letby “gaslighted” her hospital colleagues to persuade them that a rise in baby collapses was “just a run of bad luck”, her murder trial has heard.

Letby, 33, is alleged to have murdered seven children and attempted to murder 10 others on the Countess of Chester Hospital’s neonatal unit.

In his closing speech to jurors at Manchester Crown Court on Monday, June 19, Nick Johnson KC, prosecuting, said: “We want to point out the evolution of Lucy Letby’s murderous assaults on these children and we want to point out how calculated and devious she has been.

“We suggest Lucy Letby has gaslighted the staff at the Countess of Chester Hospital – doctors and nurses alike, professional people with many, many years of combined experience.

“She persuaded them what they knew in their heart of hearts to be utterly abnormal was just a run of bad luck.

“Lucy Letby got away with her campaign of violence for so long because people didn’t contemplate the remotest possibility of a nurse trying to kill tiny babies.”

Mr Johnson said the “similarities” of many of the cases involved showed a single person was sabotaging the children.

The prosecutor said: “Lucy Letby had used ways of killing babies and trying to kill them that didn’t leave much of a trace. Certainly nothing was spotted at the time as being significant and her behaviour persuaded many colleagues that the collapses and deaths were normal.

“Many of them simply couldn’t see the wood for the trees.

“Several post-mortem examinations in isolation didn’t raise the alarm because no-one – no-one – was contemplating the possibility of foul play.”

Mr Johnson went on: “We suggest Lucy Letby is an opportunist. Some of the children she targeted were sick but they would have recovered. She used their vulnerabilities to camouflage her acts.”

He pointed to the case of twin boys, Child E and F, to highlight what he said showed her “calculated” behaviour.

The Crown say Letby murdered Child E in August 2015 with an injection of air and then tried to kill Child F the next day by poisoning his intravenous feed with insulin.

Mr Johnson said two bags of nutrients were contaminated – one which Letby hung up during a night shift and a replacement stock bag used the next day when she was not at work.

Tests showed both bags – in the same fridge – contained about the same amount of insulin, the court heard.

Mr Johnson said: “It was only going to one child. It was going to be connected to that child when the poisoner was not there.

“What does that tell you about the mindset of that person?

“This is why it was a targeted attack. What better way for a poisoner to cover their tracks than to use a replacement bag to be used by an unsuspecting colleague, a member of her ‘nursing family’.

“It shows a degree of cold-blooded, cynical planning. It diverts suspicion on to someone else. It deflects suspicion from Lucy Letby.

“She undoubtedly poisoned (Child F), who just happened to be the twin of the baby she murdered the previous day.

“Cold, calculated, cruel and relentless.”

Letby, from Hereford, denies all the offences said to have been committed between June 2015 and June 2016.