Just checked one of polemical literatures written by pro-Formosus cleric, Auxilius of Naples.

 

According to Auxilius, almost in the midnight, with a roaring thunder and waves, the dead body of late Formosus emerged and travelled about a mile to the bank of River Tiber. Also, three days after, Formosus is said to appear in the vision dream of a monk and told him to retrive his corpse from the bank (Dümmler (ed.) 1866: 72).

 

Post-Carolongian Rome was in midst of factional rivalties within the city, and several such pro-Formosus polemic tracts had been written when pro-Formosus and anti-Formosus factions kept fighting each other more than 10 years after the death of Pope Formosus himself (Wickham 2015: 22, note 57). The notorious 'Cavader Synod' should be considered within this prolonging civil/ aristocratic rivalties. I'm not so sure to what extent the general crowd in Rome actually believed this 'miracle', as written in the polemic tract.

 

References:

• Dümmler, Ernst (ed.). Auxilius und Vulgarius : Quellen und Forschungen zur Geschichte des Papstthums im Anfange des zehnten Jahrhunderts. Leipzig, 1866. (Link to p.72 in question)
• Wickham, Chris. Medieval Rome: Stability & Crisis of a City, 900-1150. Oxford: OUP, 2015.

Wild, do we have any info as to what the tipping point was for the victory of the pro-Formosus camp?