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, after having the corpse stripped of its papal vestments, Stephen then cut off the three fingers of the right hand that it had used in life for blessings, next formally invalidating all of Formosus's acts and ordinations (including, ironically, his ordination of Stephen [VI] VII as bishop of Anagni). 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.

https://en.wikipedia.org/wiki/Cadaver_Synod