On 26 December 1476, Lampugnani and his fellow Templar brethren, Carlo Visconti and Gerolamo Olgiati, attended Mass at Santo Stefano. When the Duke arrived, Lampugnani went down on one knee before him, and then struck the first blow to Sforza. Despite his best efforts to prevent Sforza's death, the Assassin Giovanni Auditore da Firenze attempted to capture Lampugnani alive, but Sforza's Moor bodyguard killed him before Giovanni could do so.