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Lucy Letby’s Appeal Rejected Amidst Controversy Over Scientific Evidence

In a recent judicial decision, former nurse Lucy Letby’s application for appeal was denied, despite claims from her legal team about significant flaws in the scientific evidence used during her trial. Letby, who was convicted last year for the murder of seven infants and the attempted murder of six others, has been a central figure in one of the most harrowing cases in the history of the NHS.

The court’s refusal to grant an appeal has sparked a debate among legal experts and medical professionals. Critics argue that the scientific evidence, which played a pivotal role in securing Letby’s conviction, was fundamentally flawed. Forensic experts supporting Letby’s defense have pointed out inconsistencies and potential errors in the interpretation of medical data, which they claim could have wrongly influenced the jury’s verdict.

Despite these concerns, the appeal judges held that the original verdict was sound. The decision has left many wondering about the implications for future cases where complex scientific evidence is at the forefront.

Science on Trial: Conducting a Scientific Review of the Letby Case

Prior to Lucy Letby's conviction, Science on Trial (SoT) had conducted a comprehensive scientific review of the claims in the case ( This review was initially prepared solely for the court, anticipating that concerns might arise regarding the reliability of the scientific and medical claims made by the expert witnesses. However, our efforts were met with threats of prosecution and imprisonment, a message clearly conveyed by Justice Goss. This issue was discussed during the proceedings, \ and we were notified by Cheshire Constabulary of Justice Goss’ preliminary view that we were in contempt of court.

To date, SoT remains the only entity to present a robust scientific analysis that challenges the prosecution expert’s claims and establishes scientific standards and norms for forensic/scientific investigations. Our rigorous work attracted numerous journalists, including Rachel Aviv from The New Yorker, who used our resources extensively to report on the Letby case. Despite this, Aviv informed us that she would not cite SoT, resulting in our complete absence from her article.

The primary issue in the Letby case was the use of Infrequently Commissioned Experts (ICEs) by both the prosecution and the defense. According to the forensic sciences regulator, ICEs are experts from outside the forensic science profession who meet specific criteria, such as not being staff of a forensic unit providing services to the CJS in England and Wales and not having been commissioned in any case in the CJS in the previous 12 months. Additionally, ICEs' evidence should not be of a type that can ordinarily be obtained from a forensic unit, such as a forensic pathologist’s expertise in analyzing cause of death.

SoT in collaboration with Mark McDonald 

One element that the Letby case has brought to light is that the distinction between Science and Medicine is not effectively established in English Law. Soon after the conviction of Letby, SoT made contact with Barrister Mark McDonald and together we sought to establish the pitfalls of this lack of clarity through discussions, and potential collaborations. Briefly, Mark McDonald is what can only be described as a trailblazer in the criminal justice field with a rich history in criminal law, where at one time he was in chambers with Michael Mansfield KC, and continues to chart a unique course of criminal defense advocacy. Mark’s early years were distinct from most barristers, he was raised as an only child, by a single-mother on a Birmingham Council Estate. Mark was somewhat of an anomaly during his youth, where he grew up surrounded by a multiracial mix of West Indian immigrants who migrated to England in the decades following WWII.

It was in the defense of those charged with serious crimes that Mark found a forum to parlay those formative childhood experiences, as the one child unlike all the others,  into a genuine compassion for the underdog. Over the years, Mark has come to be viewed as one of the most vocal and committed advocates for those cases that would otherwise languish. In testament to his forthrightness and commitment to ensuring criminal justice, it was fewer than 24 hours after Lucy Letby’s verdict had been read that Mark McDonald was the lone voice in the legal community that carefully, and artfully, expressed caution in assuming that the verdicts that had been secured against Lucy Letby were  entirely safe.  Mark spoke from experience; to this day he is the barrister for two well-known cases in which serious doubts have been raised as to the safety of the convictions. The first being that of Michael Stone, the man who was convicted of being the assailant in the Russell Murders. And the more closely related Ben Geen case, another Nurse case, which bears eerily similar hallmarks to that of the Lucy Letby case. 

Given McDonald’s established history and commitment to criminal justice, SoT sought to collaborate with him to address issues surrounding scientific evidence in the CJS. In the weeks following the Letby verdict, SoT and McDonald met regularly to explore possible approaches to ensure that SoT's scientific analysis would be considered in any appellate action Letby might undertake.

We identified that an Intervention would be the primary means by which we could ensure our scientific analyses could be put before the court, where we argue that our inclusion in any appeal was in public interest. In higher courts, the Common Law Amicus curiae (Friend of the Court) submission has been refashioned under the term “Intervention.” Through consultation with Mark McDonald, SoT sought advice on the grounds for intervening in an appeal for Lucy Letby. Mark McDonald graciously assisted us in outlining the basic elements of an intervention and the terms under which we might proceed. In the early stages, both Mark and SoT firmly agreed that the combination of scientific expertise and Mark’s extensive experience in criminal defense would create a winning formula for a successful intervention.

Interventions in Judicial Review: A Prose Summary Overview

An intervener is distinct from a party directly involved in a case, such as the claimant or defendant. Unlike these parties, interveners do not have a direct stake in the outcome. Their role is to assist the court by providing information or perspectives that the parties might not offer. In the UK, this role differs from the US amicus curiae. Here, an ‘advocate to the court’ is a non-partisan figure appointed by the Attorney General upon the court’s request.

There are several types of third-party interventions:

  1. Interested Party:This party is directly affected by the case's outcome. They can be identified by either the claimant or defendant or added by the court.

  2. Amicus Curiae: This is a neutral figure who provides legal expertise or perspectives. They may act in an adversarial manner on behalf of unrepresented parties.

Public interest interventions focus on cases that raise issues of significant public importance, where the public interest may not be fully addressed by the parties involved. These interventions aim to add value to the court’s considerations. The UK Supreme Court Rules allow applications for interventions in public interest cases, ensuring that broader societal implications are considered. Although the Criminal Procedure Rules do not explicitly cover interventions in criminal cases, UK courts adopt a pragmatic approach. This approach permits interventions in the Court of Appeal on similar grounds as in judicial review proceedings.

An illustrative example is the intervention by the Office of the Children's Commissioner for England in criminal appeals involving trafficked children prosecuted for criminal offenses. The intervention focused on age assessment and ensuring the best interests of children were considered, leading to the allowance of the appeals. Applications for such interventions are made to the Lord Chief Justice, following processes similar to those in civil interventions.

Interventions in England serve to bring broader perspectives and critical insights to judicial review cases, especially when public interest issues are at stake. This approach has been pragmatically extended to criminal appeals, enhancing the court's understanding of complex issues. This is well demonstrated in cases involving vulnerable groups, such as trafficked children.

In the Letby case, ICEs were used by both the prosecution and the defense. The jury delivered a unanimous verdict on two indictments alleging attempted murder by poisoning. The defense contributed to this outcome by agreeing that available evidence indicated the infants had been victims of attempted insulin poisoning. However, according to SoT, the actual evidence, a clinical blood test result showing high levels of insulin in one assay and no detectable c-peptide in another, indicated a gross error in the test preparation, leading to unreliable results. This was detailed in prior SoT articles.

The Public Interest in the Use of Infrequently Commissioned Experts

The use of ICEs in the Letby case raises significant public interest concerns, particularly given the guidelines set forth by the forensic science regulator. These guidelines stipulate that ICEs should only be utilized when there is no alternative. In the Letby case, forensic pathologists, who are specifically trained to conduct cause of death analyses, should have been employed. This failing represents a clear violation of established standards.

ICEs, by definition, are experts from outside the forensic science profession and often lack the necessary qualifications to perform specific forensic tasks. The forensic science regulator explicitly states that ICEs should not be relied upon to develop novel, unverified scientific hypotheses, especially when these hypotheses pertain to critical determinations such as cause of death. In the Letby case, the prosecution and defense both employed retired medics as ICEs, who lacked the proper qualifications and expertise to reliably assess the evidence.

This reliance on ICEs to establish causes of death is not only procedurally flawed but also undermines the integrity of the criminal justice process. Forensic pathologists, with their specialized training and experience, are essential in providing accurate and reliable cause of death determinations. The use of ICEs in this capacity introduces a high risk of error and unreliable outcomes, which can have severe implications for the accused and the justice system as a whole.

The public interest is inherently linked to ensuring that criminal trials adhere to the highest standards of scientific rigor and integrity. When these standards are compromised, as they were in the Letby case, it erodes public confidence in the judicial system and its ability to deliver fair and accurate verdicts. It is crucial that cases involving serious allegations, such as murder, are handled with the utmost precision and reliance on appropriately qualified experts.

Mark McDonald and Legal Advocacy

Mark McDonald has experienced firsthand the distinction between science and medicine. In a recent shaken baby case, Mark explained the growing public interest issue regarding the standard of scientific evidence and the sourcing of experts in English courts: The prosecutor has a ready pool of experts who have, sometimes, decades worth of experience as expert witnesses for the Crown. Over the years, it’s been harder and harder to source experts for the defense - this harms defendants' ability to push back on prosecutor claims.

Mark highlighted a disturbing trend where defense teams in England regularly concede various factual events, creating a precarious situation for their clients.  Mark was recently asked to take on a trial involving child abuse. The prior team was in the process of agreeing to an assortment of expert findings that would diminish the mother’s ability to argue that the prosecution witnesses were wrong in their determination of harm.   Mark eventually identified suitable experts from overseas, who challenged all the prosecution expert’s assertions and ultimately the defendant was acquitted.

Due to Mark’s exceptional legal advocacy and his competency in using medical/scientific evidence in criminal defense cases, SoT sought to identify a legal team for an intervention. Mark was enthusiastic about joining such an intervention and discussed possible limitations. The central issue would be ensuring that one does not argue  beyond the public interest. So, it was essential to flesh out whether a matter conforms to those elements that are in the public interest.

Ultimately, it was decided that Mark would not make an application at that time, but would reassess the situation following the outcome of the Renewed Application for Leave to Appeal. There were many reasons for this decision, primarily concerning lack of funding, the complex legal procedure and the chances of success. Now that Letby has lost her application to appeal, the only avenue remaining for her is to apply to the Criminal Cases Review Commission (CCRC).

The CCRC serves as a safety net for defendants who have exhausted all other avenues of appeal, providing a potential path for cases to be referred back to the appeal courts if there appears to be a significant possibility of an overturned conviction. Applications to the CCRC can be based on a range of issues broader than those typically considered in direct appeals, including new evidence, arguments around the mishandling or misinterpretation of existing evidence, or any misconduct by the police, jurors, or legal representatives.

For Letby, an application to the CCRC could involve presenting new scientific analyses or highlighting flaws in the forensic evidence initially used in her trial. Additionally, if there were any inappropriate actions taken by her legal team or if procedural errors were made during the investigation or trial, these too could form the basis of her application. This broad scope allows for a comprehensive review of her case, potentially addressing any injustices that might not have been considered in the standard appeals process.


The challenges faced by SoT and Mark McDonald, exemplified by cases such as Ben Geen’s, underscore the critical issues within the English criminal justice system regarding the use of scientific evidence and expert witnesses. The reliance on ICEs and the trend of defense teams conceding to prosecution claims highlight systemic flaws that jeopardize fair trial outcomes. Additionally, the harassment and obstruction faced by SoT and Mark demonstrate the existence of a hostile environment that resists necessary scrutiny and reform.

Despite these obstacles, the collaboration between SoT and Mark McDonald aims to bring attention to these issues and advocate for the alignment of the criminal justice system with scientific standards. The necessity of independent, qualified experts and rigorous evidence assessment is paramount to ensure justice and prevent wrongful convictions. As SoT and Mark continue their efforts, their work highlights the urgent need for reform and the importance of supporting initiatives that seek to uphold the integrity of the legal system. Whether our ongoing collaborations may eventually involve assisting in an application for Letby at the CCRC is something that remains to be seen.


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