Alessandro Nencini, head of the appeals court panel in Florence that sentenced Knox to 28 1/2 years in prison and Raffaele Sollecito to 25 years in their retrial in the 2007 killing of Meredith Kercher, granted three interviews to newspapers after the verdicts, ANSA reported Wednesday.
In Italy, judges typically discuss their verdicts in written explanations published at least a month after they are announced.
Nencini was accused of not being impartial because of the interviews, ANSA said.
On Monday, Justice Minister Anna Maria Cancellieri ordered ministry inspectors to conduct a preliminary assessment. Several members of the Italian judiciary's self-governing body also requested disciplinary procedures be taken against Nencini.
"Clearly there was interference," said Sollecito after meeting with his attorney Tuesday.
In one interview, Nencini seemed to intimate that Sollecito's decision not to be questioned by prosecutors hurt his chances for acquittal.
While it was within Sollecito's rights not to be cross-examined, doing so "deprives the subject of a voice," Nencini told the publication.
Sollecito and Knox both have maintained their innocence and said they would appeal. They have already served four years in prison, including pretrial custody after their initial conviction in 2009.
The initial sentence was overturned by an appeals court. Italy's supreme court reversed the acquittals and ordered a repetition of the appeals level trial.
Sollecito surrendered his passport Friday after he took a drive through Austria, which he said was to relieve stress.
Knox stayed in her hometown of Seattle during the retrial.