maybe he could appeal - but I don't see how it could 'prove' he didn't do it
the knife, if it doesn't have blood from the victims, is just another knife with no relevance...
if it does have blood from the victims, given it was found at his home, then it is another piece of evidence against him
basically it is likely either going to be irrelevant or it is going to be evidence against him
Chewbacca is a wookie, from the planet Kashyyk...