LUCY LETBY CASE: NEW INSULIN EVIDENCE PUTS A KEY PART OF THE CONVICTION UNDER FRESH SCRUTINY

The Lucy Letby case has entered another dramatic chapter as new medical analysis challenges how one of the prosecution’s most important pieces of evidence was interpreted.

Letby, the former neonatal nurse convicted of murdering seven babies and attempting to murder seven others at the Countess of Chester Hospital, remains imprisoned and continues to maintain her innocence. Her convictions are currently being examined by the Criminal Cases Review Commission (CCRC).

At the heart of the latest controversy is the evidence surrounding insulin and two premature babies, known in the trial as Baby F and Baby L.

THE INSULIN QUESTION

During Letby’s trial, prosecutors argued that the babies’ unusually low blood sugar, combined with their insulin and C-peptide results, demonstrated that they had been deliberately given insulin.

The prosecution’s expert evidence presented the results as powerful evidence of external insulin administration.

But scientists who have subsequently reviewed the case have challenged that interpretation.

A new 100-page report submitted to the CCRC by consultant neonatologist Neil Aiton and statistician Hilde Wilkinson-Herbots alleges factual errors and omissions in key evidence presented by prosecution expert Professor Peter Hindmarsh.

That report is not a court ruling and does not establish that Letby was wrongly convicted.

But it gives the defense another opportunity to argue that the medical evidence deserves a much closer examination.

COULD NATURAL ILLNESS EXPLAIN THE RESULTS?

This is where the scientific dispute becomes crucial.

Researchers have questioned whether the insulin measurements in premature and seriously ill babies can be interpreted as straightforward proof of deliberate administration.

Some experts have argued that severe infection, critical illness and the unusual physiology of premature infants could produce abnormal metabolic findings that need to be considered before concluding that insulin was deliberately administered.

A 2026 research publication has added to those questions, prompting renewed scrutiny of the insulin evidence used at trial. The research has been presented to the CCRC by Letby’s legal team.

But there is an important distinction:

The new evidence does not prove that the babies were naturally ill, nor does it prove that Letby did not administer insulin.

It challenges whether the available laboratory evidence was sufficient to establish deliberate poisoning as confidently as the prosecution claimed.

 ANOTHER DEVELOPMENT INVOLVING A KEY EXPERT

The scrutiny has also expanded beyond the laboratory results.

In March 2026, The Guardian reported that Professor Peter Hindmarsh, the prosecution endocrinologist who gave evidence about the alleged insulin poisonings, was under a General Medical Council fitness-to-practise investigation when he testified.

The investigation involved concerns about his medical work and began on the first day he gave evidence at Letby’s trial.

A medical tribunal had imposed restrictions on his clinical practice and considered that the allegations could potentially affect his ability to act as an expert witness.

However, the tribunal still permitted him to give evidence in the Letby proceedings, and the allegations never resulted in a final regulatory finding because Hindmarsh later voluntarily removed himself from the medical register.

That revelation has generated further questions about the expert evidence presented to the jury.

It does not, by itself, invalidate his testimony or overturn any conviction.

 THE CCRC IS NOW A CRITICAL PIECE OF THE STORY

The CCRC has made clear that its role is not to decide whether Letby is innocent or guilty.

Instead, it investigates whether there is a real possibility that a conviction would not be upheld if the case were returned to an appellate court.

If the commission concludes that the legal threshold is satisfied, it can refer the convictions to the Court of Appeal.

Until that happens, Letby’s convictions remain legally valid.

 WHY THE INSULIN EVIDENCE MATTERS SO MUCH

The Letby prosecution was built around a combination of medical evidence, clinical events, staffing patterns, timing and other circumstantial evidence.

The insulin allegations were particularly significant because prosecutors argued that the laboratory results provided evidence of deliberate intervention rather than an unexplained medical deterioration.

Now the defense is asking a fundamental question:

What if those results were capable of another medically plausible interpretation?

That question does not automatically mean the entire prosecution case collapses.

But if an appellate court were eventually persuaded that crucial expert evidence was unreliable, incomplete or materially misunderstood, the consequences could be enormous.

 THE CASE IS FAR FROM OVER

For years, the Letby case was presented as one of the most shocking hospital crimes in modern British history.

Now, the focus is increasingly shifting from what happened inside the neonatal unit to how the medical evidence was interpreted in court.

New scientific research.

New expert reports.

Questions surrounding key testimony.

And a CCRC review that could eventually determine whether the case returns to the Court of Appeal.

For Letby’s supporters, the developments represent a potential path toward a historic miscarriage-of-justice challenge.

For those who believe the original convictions were correct, the new reports are arguments that still have to survive rigorous legal and scientific scrutiny.

Nothing has been overturned. No court has declared Lucy Letby innocent. But the scientific debate surrounding the insulin evidence is now more intense than ever.

And the question that could ultimately define the next chapter is simple:

Was the insulin evidence as conclusive as the jury was told — or was there more uncertainty hidden beneath the numbers?