Insulin was the count that prosecutors said did not depend on interpretation. Two babies, known at trial as babies F and L, had blood results showing high insulin and low C-peptide, a pattern the Crown told the jury could not be an accident. Nicholas Johnson KC said there was no doubt these were poisonings. Peter Hindmarsh, an endocrinologist, estimated that a fraction of a millilitre in a feed bag would do it. The unit’s insulin log did not show a matching theft, which the prosecution treated as irrelevant because so little was required. In February 2025 a different account reached the press. Geoff Chase, a professor of bioengineering at the University of Canterbury in New Zealand and a specialist in insulin dynamics in preterm babies, and Helen Shannon, a British chemical engineer, produced a long report arguing that the immunoᴀssay used at Liverpool Clinical Laboratories was not of forensic quality.

They said the Roche test is known to read falsely high when antibodies interfere, and that the laboratory’s own guidance warns it is not suitable for investigating hypoglycaemia caused by an injected dose. They also argued that insulin sticks to bags and lines, so the volume required to produce the recorded effect would be many times the drop described in court, and that no such volume was missing. Shannon said there was no scientific justification for the claim of certainty. A separate group of paediatric and toxicology specialists later told reporters the same ᴀssay should not have been left unconfirmed by a more specific method. Then, in September 2026, Chase and Shannon left the defence team.

They did not withdraw the core claim. They told the Guardian they still thought it very unlikely the two babies had been poisoned. What they would not sign was a set of further arguments being put to the Criminal Cases Review Commission, which they called inconsistent with the evidence, the science and established physiology. In a letter to the commission they said continuing to be ᴀssociated with those arguments would breach professional engineering codes in New Zealand and Britain. McDonald answered that the case does not stand or fall on one expert, and that other insulin and laboratory specialists still undermine the trial science. The fracture is the story. For a year the insulin critique was presented as the cleanest scientific attack on the verdicts, because it did not require a jury to prefer one neonatologist over another. It required them to accept that a screening test had been treated as forensic proof. The authors of that critique have now told the review body that parts of the wider case being built around their work are, in their view, not credible. A commission deciding whether there is a real possibility of a successful appeal has to weigh both facts at once: a central laboratory claim that specialist engineers still reject, and a defence file those same engineers have partly disowned.