Upvote:1
According to Wikipedia, Antipope John XVI was captured, mutilated, and then was publicly degraded in the presence of the Emperor and also of Pope Gregory V. The pope was rebuked by St. Nilus the Younger (an abbot, but as far as I know not a cleric) for his cruelty. Although it was the Emperor's troops that actually committed such horrendous deeds, Pope Gregory V effectively gave his consent by doing nothing to stop it.
While I'm not sure if other cardinals were present, it seems somewhat probable given that the Pope and Emperor were both there.