Until his death, Riario continued to aid the Borgia family in their attempts to conquer Italy, working on a map that detailed the locations of the pages of Altaïr Ibn-La'Ahad's Codex. In 1488, Caterina hired Checco and Ludovico Orsi to murder her husband. The Orsi brothers infiltrated Riario's home, stabbed him to death, and looted his residence. Riario's naked corpse was then thrown in the center of the town square.
His son, Ottaviano, succeeded him as Lord of Imola and Forlì, with Caterina Sforza serving as regent.