Ya, looks like the smoking gun is nuanced DNA testing on knife.
I remember reading this before and it chilled me. People take DNA results very seriously (as they should), but the results are only as good as the testing methodology, the collection, the handling, and the rigorous attention to making sure everything is done within the exact protocols of the test.
"Do overs," trying to make DNA match a suspect when at first they didn't or there wasn't enough DNA to match should make everyone nervous. Makes you think they weren't very confident about the rest of their evidence to put so much pressure on this knife.
Sounds a lot like someone who needs the evidence to match the theory, doesn't it? That Mignini is bad news, all the way around.