On 26 December 1476, Visconti and his fellow Templar brethren Giovanni Andrea Lampugnani, Lampugnani's servant Franzone, and Gerolamo Olgiati, attended Mass at the Santo Stefano. After Lampugnani had delivered the first blow to Sforza after the latter's arrival, the others followed him with their attacks. While Lampugnani was killed shortly after by one of Sforza's guards, Visconti, Olgiati, and Franzone managed to escape, only to be caught and executed within the next week after Franzone was captured and disclosed the identities of the other two while under torture.