High insulin levels in babies - used to convict UK nurse Lucy Letby - could have occurred naturally.
A jury found the 35-year-old guilty of the murder or attempted murder of 14 babies.
Some experts have suggested in a report that the deaths could be from errors or natural causes.
Canterbury University professor, Geoff Chase, assisted in the report.
He says Letby was found guilty of adding insulin to two babies' intravenous food - and their levels were unexpected, but not impossible.
He also explained their levels were unexpected, but not impossible - and in pre-term newborns, most to all bets are off.
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