He is right. Letby was convicted on purely circumstantial evidence and many experts are doubting validity of the verdict
"MP tells parliament he believes justice has not been done after hearing experts’ concerns over former nurse’s murder convictions"
https://www.theguardian.com/uk-news/2025/jan/08/lucy-letby-retrial-needed-after-clear-miscarriage-of-justice-says-david-davis