I think Letby's absolute normality was the key to her success, she wasn't suspected and perhaps most terrifyingly of all, she was caught by maths. I don't quite lean into the idea that if she was male she wouldn't have got away with it - Shipman was caught eventually (also by maths) and I think there are plenty more like Letby out there. Had Letby managed to control herself, she could've killed a statistically average number of babies every year for the rest of her life. It's chilling. My thoughts are here if you're interested. https://medium.com/p/3452284bf052