Yes, I agree that they should have done more in depth testing. However, the very high insulin level coupled with the low C Peptide is important. If the insulin had been produced by the baby themselves, the C Peptide would be correspondingly high - but it wasn’t at all. Therefore the deduction was external administration of insulin.
As I understand it, there is a test that could have spotted that the insulin was engineered rather than natural insulin from the pancreas, and that test wasn’t done, but I can’t see any other credible answer to the high insulin/low C Peptide than that the baby was given insulin. The prosecution said this insulin was in a feed bag which would account for the sudden and severe hypoglycaemia, and the hypoglycaemia halted when the feed bag was changed.
I guess what I’m saying is that there might have been another test that could have been done in addition, but that this test seems pretty conclusive. Even Letby herself agreed that the baby had been given insulin but denied it was her who did it.
I think the alleged method of administration via feed bag, and the huge amount of insulin, is different from usual factitious insulin administration, which would be given by subcutaneous injection and lead to much smaller levels of insulin in the blood than were found in this baby.