A neonatal nurse has been found guilty of murdering seven babies and attempting to kill six more, making her the worst child serial killer in modern British history and raising urgent questions over whether her crimes could have been stopped. Lucy Letby, 33, was convicted of the “persistent, calculated and cold-blooded” murder of five premature boys and two newborn girls on the unit where she worked at the Countess of Chester hospital in north-west England. As ministers ordered an independent inquiry into how Letby was able to carry out her horrifying campaign, a whistleblower told the Guardian that he believed babies would have been saved if hospital executives had acted sooner on concerns about the nurse. Dr Stephen Brearey, who was the first to alert executives to Letby’s connection to unusual deaths and collapses, said he felt bosses had been “neglectful” by failing to contact the police earlier. Letby was in her mid-20s when she preyed on highly vulnerable babies between June 2015 and June 2016, often attacking them just moments after their parents or nurses had left their side. Police were finally contacted in 2017 and she was arrested in 2018. Her victims included two identical triplet brothers, killed within 24 hours of each other, a newborn weighing less than 1kg (2lb) who was fatally injected with air, and a girl born 10 weeks premature who was murdered on the fourth attempt. Bereaved parents gasped and wept in the public gallery as the verdicts were delivered over several dramatic days at Manchester crown court, after one of the longest-running murder trials in recent times. Outside court, parents of the victims said justice had been served but that no conviction would “take away from the extreme hurt, anger and distress that we have all had to experience”. Letby is expected to become only the third woman alive in the UK to be handed a whole-life term – meaning she will never be released from prison – when she is sentenced on Monday. Police believe Letby may have harmed more babies during her six-year career as a children’s nurse and have launched a helpline for parents to call to report concerns. Detectives have asked specialists to examine the records of more than 4,000 infants born at Liverpool Women’s hospital and the Countess of Chester, the two hospitals where Letby worked between 2010 and 2016. One mother said on Friday night that she believed Letby attacked her newborn son a day after she made a complaint about an “inappropriate” comment by the nurse. Lynsey Artell, who was herself a nurse at the Countess of Chester at the time, told Sky News that Letby was eavesdropping on a conversation about the progress her son was making, when she said: “I don’t like parents getting their hopes up because we never know what could happen at this stage.” Artell said she was “furious” and complained. The following day, she said, her son suddenly deteriorated and his insulin levels had spiked – just like in the cases of two babies Letby was convicted of poisoning. She said police had investigated her son’s decline but decided not to bring charges. Pascale Jones, a senior prosecutor at the Crown Prosecution Service, said Letby’s attacks were a “complete betrayal” of the trust placed in her and that she had “perverted her learning and weaponised her craft to inflict harm, grief and death”. Letby refused to return to court to hear the later verdicts but at an earlier verdict hearing had bowed her head and sobbed while her mother, Susan, cried loudly and said: “You cannot be serious. This cannot be right.” The trial heard how Letby murdered newborns by injecting air into their tiny bodies, in some cases shattering their diaphragms, or in one case by pushing a tube down an infant’s throat. She tried to kill two babies by lacing their feeding bags with insulin. DCI Nicola Evans, of Cheshire constabulary, described her as a “calculated and callous” killer who had acted “under a cover of trust”. She said: “Lucy Letby was operating in plain sight. She abused the trust of the people around her. Not just the parents that had entrusted her with their babies but also the nurses she worked with and the people that she regarded as friends.” One of the babies was the size of an adult hand, weighing just over 535g (1lb), when she was born 15 weeks premature and given a 5% chance of survival. Letby tried to kill the girl twice – the first attempt just hours after she and the family had marked her 100th day of life with a celebratory cake, and the second on what would have been her due date two weeks later. Letby was found not guilty of a third count of attempted murder against her. The little girl, known as Child G, was diagnosed with quadriplegic cerebral palsy after the attacks. Now eight, she is nil by mouth and requires 24-hour care. Her parents gasped when the guilty verdicts were returned to a packed and silent courtroom. They handed out tissues, as relatives of the other victims cried and held each other. The mother of twin boys, who walked in on Letby attacking one of her sons, bent over and sobbed as the nurse was found guilty of murdering one of her six-day-old babies and attempting to kill his brother the following day. The verdicts were delivered over several days but can only now be reported following the end of jury deliberations lasting more than 110 hours across more than four weeks. Another baby was 24 hours old when Letby injected him with air, killing him just 90 minutes after she had started her shift. She tried to kill his twin sister the next day. None of the victims or their families can be named for legal reasons. Letby consistently denied the charges, telling jurors she was “devastated” by the allegations and: “I only ever did my best to care for them. I’m here to help and to care, not to harm.” But after a trial lasting 10 months, the jury of seven women and four men decided she was guilty of attacks that the prosecution described as “persistent, calculated and cold-blooded”. Parents of two of Letby’s victims said the nurse behaved strangely as they spent their final moments with their murdered babies. The mother of a newborn girl, who weighed about 1kg at birth, recalled Letby “smiling” and offering to take photographs as they bathed their daughter. She later sent the family a sympathy card and took a photograph of it on her phone. Another parent told the trial that a nurse he believed to be Letby interrupted their final moments with their little boy by trying to place him in a ventilator basket, meant for dead babies, even though he was still breathing. She allegedly told the grieving parents: “You’ve said your goodbyes. Do you want me to put him in here?” The medical director at the Countess of Chester hospital, Dr Nigel Scawn, said: “We are extremely sorry that these crimes were committed at our hospital and our thoughts continue to be with all the families and loved ones of the babies who came to harm or died. Our staff are devastated by what happened and we are committed to ensuring lessons continue to be learned.” In total, Letby was found guilty of seven counts of murder and seven counts of attempted murder. The attempted murders relate to six babies as multiple counts apply to some of the infants. She was found not guilty of two counts of attempted murder. The jury was unable to reach verdicts on six further counts of attempted murder, relating to five babies. The CPS is considering whether to seek a retrial on those charges. Janet Moore of Cheshire police said on the relatives’ behalf: “Some families did not receive the verdict that they expected and therefore it is a bittersweet result. We are heartbroken, devastated, angry and feel numb. We may never truly know why this happened.”