The tests that should have been done — and were not
Prosecution claim
The Crown's case relied on the tests that were done: the Roche Cobas insulin immunoassay, post-mortem macroscopic examination, and clinical observation. The jury was told these were sufficient to establish deliberate harm.
Counter-evidence
In every comparable case worldwide, forensic-standard exogenous-insulin cases proceed on confirmatory mass spectrometry from a validated forensic laboratory (in the UK, Guildford). The Letby samples were processed at the Royal Liverpool laboratory under a clinical — not forensic — protocol: gel tubes, delayed centrifugation, ambient-temperature storage. Confirmatory mass spectrometry was never performed. Nor was post-mortem imaging (CT or radiograph) that would show intravascular gas if air embolism had occurred. Nor were TPN bags retained for forensic testing. The absence of these tests is not an incidental gap — they are the tests that would actually answer the forensic question. Their absence is itself evidence.
You cannot convict on the tests that were done while ignoring the tests that were not done but should have been. The missing forensic chain of custody is part of the record.
What the jury heard
The jury heard what the prosecution's witnesses reported from the tests that were actually done. The jury was not systematically walked through the tests that would have been required to reach a forensic standard.
What the Panel says
The Panel concludes that the absence of mass spectrometry confirmation on the insulin samples, the absence of post-mortem imaging of the type that would show intravascular gas, and the absence of retained TPN bags for forensic chemistry, together mean the medical evidence does not meet a forensic standard for any of the charged mechanisms.
What independent experts add
- Mass spectrometry is the standard confirmatory test for exogenous insulin. It was not done.
- Post-mortem radiographs were not systematically obtained in the cases where air embolism was alleged. CT would have shown gas in cardiac chambers or vasculature if it had been present.
- TPN bags alleged to have been spiked with insulin were not retained for forensic chemistry. There are therefore no physical exhibits for the insulin allegation.
- Sample chain of custody for the insulin tests did not follow forensic-laboratory protocols. The Liverpool laboratory's own 2012 protocol (replacing the 2010 protocol in force at the time) acknowledges that it cannot diagnose exogenous insulin.
- Histological findings that would distinguish air embolism at autopsy from artefact of tissue handling were not systematically obtained or discussed at trial.
- The defence position was that the missing tests should be fatal to the prosecution allegation. The jury was not walked through this argument in the detail the Panel's 2025 review does.