On 26 December 1476, Olgiati attended the Mass at Santo Stefano in Milan, with several of his Templar brethren hidden in the crowd.
Lampugnani was first to approach Sforza, and stab him with a dagger hidden in his boot. Olgiati quickly followed suit, and stabbed Sforza in the back. At this point, a battle between the Templar assassins and Sforza's guards commenced.
All the assailants except for Lampugnani managed to escape, only for Olgiati, Visconti and Lampugnani's servant Franzone to be caught and executed within a week, after the latter had been caught and disclosed information under torture.