The families of the babies killed by the British nurse Lucy Letby spoke of their search for answers and “extreme hurt, anger and distress” after she was found guilty of murdering seven newborns and the attempted murders of six others.

Letby, who was in her 20s at the time of the murders, is the most prolific child serial killer in modern British history.

Her case captivated Britain after she was put on trial for the killings and attempted murders in the neonatal unit of a hospital in northwest England where she worked.

Following her conviction at a court in Manchester in northern England on Friday, the families released a joint statement saying they would never truly know why this had happened.

“To lose a baby is a heartbreaking experience that no parent should have to go through,” they said. “But to lose a baby or have a baby harmed in these circumstances is unimaginable.”

The families cannot be named for legal reasons. The parents of the twin boys who Letby tried to murder revealed the turmoil that they had been through, going from the euphoria of the birth to the horror of seeing staff fight to keep their children alive.

They did not realise what had happened until the police contacted them about two years later.

“It didn’t have to be that many,” the father told Sky News, asking why hospital bosses had not acted sooner to stop more babies from being attacked. He said he felt “very let down” by the hospital.

Letby was present at the birth of the two boys and the parents said they were ecstatic at being first-time parents.

But the mother realised something was wrong when another nurse came into her room, saying she needed to come downstairs. The father said he remembered seeing the doctors pumping his child’s heart “like a rag doll”.

“I was just full of tears,” he said. “We didn’t know what was going on.”

He remembered how other nurses looked “very worried and panicked” while Letby was standing “very calm and cool”.

Both the twins survived, but one suffered some brain damage and his parents worry it might impact him in the future.

The boy’s father said he is now a “changed person” and suffers sleepless nights and depression.

The government has ordered an independent inquiry, including how concerns raised by clinicians were dealt with.

Who is Lucy Letby?

Letby, 33, was born in Hereford in central England. She completed a nursing degree at Chester University in northwest England and after qualifying, she began to work in the neonatal unit of the city’s Countess of Chester Hospital.

What is the case about?

Over 18 months from January 2015, there was a significant rise in the number of babies dying and suffering serious collapses at the neonatal unit of the Countess of Chester Hospital.

Senior doctors became worried as many of the babies had deteriorated suddenly and unexpectedly, and then did not respond to appropriate resuscitation. Other babies, who suddenly collapsed and did not die, recovered, with both their collapse and recovery defying usual medical norms.

The police and medical experts were called in and as they looked for a cause, they eventually focused on one common factor - Lucy Letby.

She was first arrested in July 2018, and then again in June 2019 and November 2020 when she was charged with murdering seven babies and attempting to kill another 10 between June 2015 and July 2016.

What was Letby accused of doing

Prosecutors said Letby attacked 17 babies who had been on the ward. Some she was said to have poisoned with insulin. Mostly she was accused of injecting air into their bloodstream or stomachs, or giving them excessive milk.

The victims included twins and in one case, she killed two siblings on consecutive days. The youngest baby she murdered was just a day old. The oldest was 11 weeks old, a baby girl who she attacked four times before succeeding in killing her.

Although the babies had been born prematurely, some were regarded as being in reasonable or good condition before they suddenly deteriorated, mainly during night shifts when Letby was working.

Letby attacked a number of the babies shortly after their parents had left their bedside, prosecutors said.

She denied any wrongdoing and blamed the hospital and doctors working there. But a jury convicted her of seven murders and seven attempted killings. Two of the attempted murder convictions refer to the same baby.

She was acquitted of two charges of attempted murder while jurors could not agree on six other suspected attacks.

Why did Letby attack the babies?

Police said they had been unable to find a motive for the attacks, saying their focus had been on providing answers to the parents and families of her victims.

“Unfortunately, I don’t think we’ll ever know unless she just chooses to tell us,” said Detective Superintendent Paul Hughes, who led the investigation.

What was Letby like?

Detective Chief Inspector Nicola Evans, the deputy senior investigating officer, described Letby as “beige”.

“She had a healthy social life, she had a circle of friends, she had her parents and holidays, and there isn’t anything unusual in any of that, there isn’t anything that we have found that has been unusual,” Evans said.

She said there was nothing the police could find that was unusual for a woman of her age at that point in her life.

Are there other victims?

Police said they were reviewing Letby’s career prior to the period covered by the charges, at the Countess of Chester Hospital and at the Liverpool Women’s Hospital where she had spent part of her training.

Detectives are looking at the more than 4,000 admissions made into the two hospitals’ neo-natal units from 2012 to 2016.

“This does not mean we are investigating all 4,000, it just means that we are committed to a thorough review of every admission from a medical perspective, to ensure that nothing is missed throughout the entirety of her employment as a nurse,” Hughes said.

“Only those cases highlighted as concerning medically will be investigated further.”