The prosecution case that Lucy Letby murdered a number of babies is founded on guesswork and is “tenuous in the extreme”, her barrister has told a court. Benjamin Myers KC said the evidence against the nurse was so poor it could not be safely used to support the allegations of murder and attempted murder. Letby, 33, from Hereford, denies murdering seven babies and attempting to murder 10 others between June 2015 and June 2016 at the Countess of Chester hospital where she worked. The children’s nurse allegedly targeted a number of the infants by injecting air into their bloodstream. The prosecution claim this caused an air embolism which blocked the babies’ blood supply and led them to deteriorate rapidly and suddenly, with some proving fatal. In his closing speech in Letby’s defence, Myers asked the jury of eight women and four men to consider how the theory of air embolus worked in this case. “This is meant to be reliable, scientific medical theory, underpinning the most serious allegations,” he said. “At the heart of it are prosecution experts Dr Dewi Evans and Dr Sandie Bohin. They are the ones we say are pushing it and the prosecution rely on it, of course. “Neither of them has clinical experience in identifying or treating air embolus.” He said both had principally relied on a research paper written more than 30 years ago about the effect of air embolism on infants. That study, said Myers, showed 11% of 53 children had displayed signs of skin discolouration. In several cases there were “blanching and migrating areas of cutaneous pallor”, the court heard, and in one case there were “bright pink vessels against a generally cyanosed cutaneous background”. Myers told the jurors: “As a basis for conviction for someone of murder and attempted murder it is tenuous in the extreme. “That meagre piece of research has carried into guesswork in this case.” Myers said both experts had made “extraordinary contortions” to fit the theory that the babies had been deliberately injected with air. “Scientific evidence needs to be sufficiently reliable if you are going to rely on it,” he said. “What guidance you have had from the experts has been applied inconsistently throughout the case. “The evidence is so poor it cannot be safely used to support these allegations.” The trial continues.