Now, reasonable people do understand that the blood passport is not 100% effective weeding out blood doping. A conviction has to show beyond any reasonable doubt (or whatever the legal phrase is) that blood doping has taken place. So, in order to minimize the 'false positives', you sacrifice quite a few 'true positives' (which then end up in the 'false negatives' category).
Just because we cannot, beyond any doubt, say that Contador did transfuse, it does not follow that he definitely didn't transfuse. Even lawyers, journalists and PR people should be susceptible to that much logic.