Claudio Pratillo Hellman, who read the verdict Monday that cleared Knox and her Italian boyfriend, Raffaele, Sollecito, said Rudy Guede, the only person now convicted of the killing, is also the only person who can say whether he acted alone, the Italian news agency ANSA reported.
"It will remain an unsolved mystery. Nobody can say what the facts are," Hellman said. "The only one is Rudy Guede."
Guede, an immigrant from Ivory Coast, was convicted at a separate fast-track trial and is now serving a 16-year sentence. There was much stronger evidence against him than against Knox and Sollecito, and he has lost all his appeals.
Prosecutors say they will appeal Monday's verdict. But Knox, a student at the University of Washington when she was arrested, has returned to Seattle and extradition could be difficult.
Notable deaths of 2014 [PHOTOS]