If there are other culprits then I certainly share your hope that they will be brought to justice. However, I see no reason to believe that anyone other than Rudy Guede was responsible for this murder, and you have given me no reason to believe any such thing either. All you've given is an appeal to authority, but no court has divine infallibility, no not even the highest court in Italy.
The only logical reason to believe that Rudy Guede did not act alone is the fact that the highest court in Italy, after reviewing all of the evidence, came to this conclusion. I'll accept that as fact.
Regarding the apparent skepticism regarding the rulings in Italian courts ... are you equally skeptical about the decision to set Knox and Sollecito free, or are you only skeptical of the rulings when they don't fit a particular theory.