Talk about strong encryption. It took five centuries to untangle the code in a letter written by a previously unknown collaborator in a famous Italian Renaissance murder plot.The Pazzi conspiracy, named for a wealthy Florentine banking family, was audacious. Its targets: Lorenzo de\u2019 Medici and his brother Giuliano, who were ruling elites in Florence. The place: The city\u2019s cathedral, during high Mass on April 26, 1478. The goal: End the Medici rule over Florence while giving Pope Sixtus IV more power in the region.The plot failed?Lorenzo survived his stab wound, though Giuliano died, the Columbia Encyclopedia tells us. The Medici\u2019s reign continued. Florentines hunted down the conspirators to exact revenge. Except that they missed one. Now, 526 years after the deed, Marcello Simonetta, a Wesleyan University Romance language professor, has uncovered and then deciphered an encrypted letter written by one Federico da Montefeltro, the Duke of Urbino, a prominent politician and famous art collector. The duke, it turns out, was a key coconspirator who offered troops to Sixtus IV to help kill the Medicis. He sent the letter two months before the murder.The duke "was known as one of the most refined men of the Renaissance," Simonetta told The New York Times. That was before the professor cracked the code.