Jean Paul Laurens - Le Pape Formose et Etienne VII: Concile cadavérique de 897, 1870

Probably around January 897, Stephen (VI) VII ordered that the corpse of his predecessor Formosus be removed from its tomb and brought to the papal court for judgement. With the corpse propped up on a throne, a deacon was appointed to answer for the deceased pontiff. Formosus was accused of transmigrating sees in violation of canon law, of perjury, and of serving as a bishop while actually a layman. Eventually, the corpse was found guilty. Liutprand and other sources say that Stephen had the corpse stripped of its papal vestments, cut off the three fingers of his right hand used for benedictions, and declared all of his acts and ordinations (including his ordination of Stephen (VI) VII as bishop of Anagni) invalid. The body was finally interred in a graveyard for foreigners, only to be dug up once again, tied to weights, and cast into the Tiber River. According to Liutprand’s version of the story, Stephen (VI) VII said: “When you were bishop of Porto, why did you usurp the universal Roman See in such a spirit of ambition?

source: Wikipedia