"Even taken all together," the prosecution's evidence does not "prove in any way the guilt of Amanda Knox and Raffaele Sollecito for the crime of" killing British student Meredith Kercher, Judge Claudio Pratillo Hellman wrote in legal paperwork made public Thursday, CNN reported.
Knox and Sollecito were convicted of murder in 2009 in the death of Kercher, but both were cleared on appeal in October.
Prosecutors said they would probably appeal the acquittal.
In Italy appeals cannot be filed before the judge publishes a report, known in Italian as a motivazione, or motivation, regarding a jury's reasoning for its verdict, CNN reported.
Knox's attorney said he was "fully satisfied" with the judge's report.
"We've always said that there was no evidence, that the first court ruling was based on probabilities and not facts," Carlo Dalla Vedova said. "The first ruling was a mistake, which has now been corrected, so we are very satisfied with it."
A third man, Ivorian drifter Rudy Guede, was convicted of the killing in a separate trial.