Issues of reliability occur where the interpretation of scientific evidence is highly dependent on human judgement.
Scientifically, the case against Ms Letby has not been proven. The major scientific evidence presented to the jury amounted to two blood tests and x-rays. All the other evidence relies on significant interpretation by expert witnesses, and the reliability of these witnesses is questionable given that they overlook clear pathological symptoms which are reported in the literature. For example, the bruising of the liver, is a widely appreciated phenomena, which is associated with prematurity, and sepsis. Likewise, internal bleeding is not regularly associated with air embolism, yet a number of children exhibited significant signs of internal bleeding. Questions should be asked as to how such minimal medical evidence can be used to convict a person of murder and attempted murder, least of all when the original autopsies performed do not correspond with the alleged cause of death.
A number of factors can contribute to a lack of reliability surrounding the scientific evidence. These issues can deprive both prosecution and defence of any robust scientific reasoning necessary to present their cases.
Failure to conduct appropriate post mortem examinations: In 6/7 deaths post-mortem exams showed that the infants died of natural causes. There is no published announcement that a request for a second post-mortem exam was made to the coroner.
Cheshire Constabulary retained a retired paediatrician, whom at the time of carrying out the investigation was not registered with the GMC, which barred him from acting as an expert.
Failure to use standard expert witnesses: The Letby case represents a highly unusual approach to carrying out a murder investigation, where no home office pathologists are used, and the investigation is apparently outsourced to a retired medical doctor, and the doctors who were present at the crime scene at the time the victims either died or were attacked.
Conflation between murder and attempted murder The same physiological events are used as proof of murder and attempted murder without any physiological rationale. There is a denial of the relevance of preterm neonatal physiology, and a failure to caution on the differential diagnoses. Few of the children received appropriate diagnostic workup and testing by the clinical team which skews the reliability of the claims to suddenness. All deaths are sudden and unexpected where doctors fail to carry out appropriate testing.
Desaturations are used as a proof of harm, but desaturations occur for numerous reasons and are not indicative of any specific physiological event in isolation.
Suspects as witnesses. Child neglect is a crime, thus all individuals involved in the care of the infants should be minimally suspected of child neglect. This standard is applied in other cases, where individuals attending a crime scene in which a murder takes place are also charged with the offense, under the principle of "joint enterprise." Despite doctors being present at the time of death of all the infants, and where the consultants claim they suspected the defendant of murder no action was taken to report her, or inform the coroner of potential foul play, thereby necessitating an inquest.
The doctors are now claiming that they were whistleblowers and were prevented from contacting the police. However, these claims do not comport with their testimony at trial, where Dr Gibbs said that they only suspected Lucy Letby after they identified the insulin poisoning cases. This occurred in 2018, a year after police were involved.
Inviting Jury to accept untested hypotheses as possible events: A blood test is used to infer harm to a child, where no harm was suspected at the time, nor is there any indication that the high insulin resulted in harm.
The blood test does not show proof of exogenous insulin nor any other agent, the blood test demonstrates the low detection of a specific protein, c-peptide, which in healthy children and adolescents is expressed in a ratio with insulin which is typically greater than 1. The absence of the ratio observed in children and adults is used to infer the presence of exogenous insulin.
The case spirals out of control surrounding the insulin poisoning claims, and the approaches taken stand in stark comparison with the Beverley Allitt case where stringent testing was undertaken.
Lack of evidence is used as proof of guilt. The failure to take proper or accurate observations of the infants is used as a means to claim that the infants were fit and healthy. There are no positive indicators that the infants were as such, and prematurity is associated with increased morbidity and mortality. If the proportion of premature births increased in this period we would expect mortality to increase, we have no insight into trends other than Letby’s shift data.
Inviting jury to speculate: Cause of death is treated as irrelevant when determining murder charges, though the cause of death is indicative of the likelihood of murder.
In advising the jury with regard their deliberations, Mr Justice Goss stated:
““In the case of each child, without necessarily having to determine the precise cause or causes of their death and for which no natural or known cause was said to be apparent at the time, you must be sure that the act or acts of the defendant, whatever they were, caused the child’s death in that it was more than a minimal cause.”
It is apparent that the jury was expected to take incomplete scientific evidence, which was not evaluated by expert witnesses with the requisite expertise, and speculate as to whether the scientific theories presented by the expert witnesses were sufficient to find Lucy Letby guilty of murder. Suffice to say, no credible scientist would even be able to speculate, as to guilt or innocence, on such a weak evidentiary basis, even where they could rely upon their scientific knowledge. To invite lay people to do as such guaranteed that Lucy Letby would be subject to an unfair trial, and that any conviction procured on this basis was fundamentally unsafe.
Many of these issues will be important in forming the basis of an appeal.