Im very sure Vito would kill fannucci wether he was connected to the black hand or not. I mean its not in the movie this scene, so if you only watch the final cut, then vito just simple decides to kill him. Also I'm not sure if fannucci is losing credit as a gangster when he is mugged by thugs. I mean, he seem's confident to take on those little punks and is playing with them almost. Then out of nowhere he gets cut.

I dont remember fannucci looking in his direction...perhaps a little down. To me it seemed like he did not see anyone there...i mean Vito is hiding and fannucci is running by screaming, so that would seem weird if he saw him all along.

Peace

CCDevlin