The Hidden Blade Assassin's Creed in Depth

The developers try to force an Exposed assassination of Vieri de' Pazzi. If you climb up his tower, you'll become Exposed when you reach the top, regardless of whether they can see you.

Let's try a different strategy - Let's use throwing knives to remain undetected. You are too far away from Vieri to lock onto him, so you have aim for him "manually." Ezio throws knives in his last direction of horizontal travel. To horizontally aim your throw, just walk ahead and fine tune your direction of movement so that Vieri appears just over Ezio's head. The vertical aim of the throwing knife is determined by Ezio's altitude when it is thrown. Throw 2 knives as you approach the apex of the roof to get the correct vertical aim.