Because there's enough reasonable doubt, that our criminal court system goes by, for Peterson to get off..
Just because I'm positive someone did it, doesn't necessarily mean they will be convicted
OTOH, over the months of reading posts from some very intelligent FReepers, I've had to conclude a couple of the twelve jurors might not convict. If they couldn't convict from strong circumstantial evidence, they shouldn't have served on this particular jury, IMHO.
sw