- "At the altar, when the echo of the choir becomes loud, and the bell rings for the twelfth and last time, the Duke of Milan will die!"
- ―Rodrigo's ally, after being tortured by the Medici, 1476.[src]
As Rodrigo Borgia and his men left Florence on foot by night, they were attacked by the Assassin Giovanni Auditore da Firenze. Rodrigo himself retreated while his men were easily dispatched by Giovanni. The Assassin captured one and took him prisoner to the home of his employer, Lorenzo de' Medici, for questioning.
Tortured on a rack by Uberto Alberti and the Medici's men, the prisoner revealed their plans: Galeazzo Maria Sforza, the Duke of Milan and a powerful ally of the Medici, was to be murdered in the Basilica di Santo Stefano Maggiore on Boxing Day, during the Saint Stephen's Day Feast. Lorenzo immediately ordered Giovanni to leave for Milan to thwart their plans.
Feast of Santo Stefano
A crowd of onlookers watched as Duke Sforza entered the church, surrounded by his bodyguards. Giovanni watched from the crowd, then entered the church via the rooftops to avoid attention. Once inside, Giovanni spotted the killers: Giovanni Andrea Lampugnani, Gerolamo Olgiati, Carlo Visconti, and two other men.
Once the Duke completed his prayers, Lampugnani approached and kissed the duchal ring before plunging a dagger into the Duke's abdomen. Olgiati and Visconti also attacked the Duke, as the conspirators' own men engaged the Duke's bodyguards in combat. Giovanni assisted Sforza's men in the fight, but the Duke himself was already dead at the altar. Lampugnani immediately tried to escape, only to be killed by Sforza's Moor bodyguard.
When Giovanni inspected Lampugnani's effects, he discovered Venetian ducats in the man's coin purse. Giovanni then left Milan to investigate the Duke's murder and bring all the conspirators to justice.
With the loss of Duke Sforza, the Florentine Medici had lost a powerful ally. This left the city more vulnerable to a Templar takeover.