After the fall of the Assassins in Monteriggioni, Cesare Borgia tasked Pietro with the retrieval of the secret artifacts hidden underneath Villa Auditore. Pietro's mission lasted a few years because he spent his initial time in Monteriggioni befriending the locals and earning their trust. At one point, the elderly father of an Assassin came to him with a broken hand for treatment. The old man, too trusting of Pietro, revealed his son's operations in Rome during a casual conversation. Believing this to be the lead he needed, Pietro knocked the man unconscious before dragging him to his cellars to be tortured for more information.
Once his prisoner broke, Pietro learned of a secret entrance that led to a chest holding the blueprints to the Corvix Blade designed by Demetrio il Silente. To ensure the success of his theft, he needed to divert the attention of Lo Sparviero, the only Assassin left to safeguard the city. He employed three mercenaries to disguise as tax collectors and harass the residents. Through bribery of the Captain of the Guards, the local soldiers even protected the mercenaries and enforced their extortion. As expected, Lo Sparviero acted to defend the citizens, assassinating all three thugs, but falling prey to the ruse and allowing Pietro to retrieve the chest.
Two days after this affair, the elderly man managed to escape from the cellar and alert the citizens to Pietro's treachery just before the Templar had planned to depart from the town. Overwhelmed by the sudden public backlash, Pietro rallied his henchmen at the front of the local church for protection, where he was identified by Lo Sparviero through Eagle Vision. Spotting the Assassin at the exact same time, Pietro fled to the villa, where he hoped the bribed guards could defend him. This proved to be futile as Lo Sparviero was able to sneak past the guards and assassinate him from behind.
Shortly after the Assassins Ezio Auditore and Leonardo da Vinci discovered the Temple of Pythagoras in 1506, an Assassin scout discovered the chest hidden in the catacombs used to enter that temple. When three Assassins were sent by Niccolò Machiavelli to help this scout retrieve the chest, all were ambushed by the Templars and killed.
In his grief, Machiavelli sent Lo Sparviero to not only recover the chest but to also avenge their deaths. Lo Sparviero succeeded where his four comrades had failed, all within an hour. It was not until after they retrieved the chest and rescued Demetrio that the Assassins learned what Pietro had stolen many years before.