The Cadaver Synod

"The Cadaver Synod (also called the Cadaver Trial; Latin: Synodus Horrenda) is the name commonly given to the ecclesiastical trial of Pope Formosus, who had been dead for about nine months, in the Basilica of St. John Lateran in Rome during January 897.^[1] The trial was conducted by Pope Stephen VI, the successor to Formosus's successor, Pope Boniface VI. Stephen had Formosus's corpse exhumed and brought to the papal court for judgment. He accused Formosus of perjury, of having acceded to the papacy illegally, and illegally presiding over more than one diocese at the same time.^[2] At the end of the trial, Formosus was pronounced guilty, and his papacy retroactively declared null.^[2]

Probably around January 897, Stephen VI ordered that the corpse of his predecessor Formosus be removed from its tomb and brought to the papal court for judgment. 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. According to Liutprand, Stephen VI said: "When you were bishop of Porto, why did you usurp the universal Roman See in such a spirit of ambition?"^[21]

Eventually, the corpse was found guilty. Liutprand of Cremona 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 his ordination of Stephen VI 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.

The macabre spectacle turned public opinion in Rome against Stephen. Formosus's body washed up on the banks of the Tiber,^[22] and rumor had it that his waterlogged rotting corpse was still performing miracles. A public uprising deposed and imprisoned Stephen. He was strangled in prison in July or August 897.^[23]

In December 897 Pope Theodore II (897) convened a synod that annulled the Cadaver Synod, rehabilitated Formosus, and ordered that his body, which had been recovered from the Tiber, be reburied in Saint Peter's Basilica in pontifical vestments. In 898, John IX (898–900) also nullified the Cadaver Synod, convening one synod in Rome, and another in Ravenna. The two synods which affirmed the findings of Theodore II's synod, ordered the acta of the Cadaver Synod destroyed, excommunicated seven cardinals involved in the Cadaver Synod, and prohibited any future trial of a corpse.^[24]"

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