In Assassins Creed 2 why does petruccio need feathers

If you find all of the feathers you receive an achievement/trophy.

You also receive a special cape, this one for the Auditore family. It renders you entirely notorious at all times while you wear it. This is useful because you can walk into a city with no notoriety, put on the cape, kill someone, take off the cape, and have no notoriety- the actions are blamed on the cape wearer, whom they don't believe is you.