Logically, since Vito moved in immediately or almost immediately to take over Fanucci's rackets, and no one else challenged him, everyone would assume he'd killed Fanucci.
Most probably TB. Fanucci is murdered and then Vito, Clemenza, and Tessio start showing up in Fanucci's prior capacity. The people in the neighborhood put 2 and 2 together.
"Generosity. That was my first mistake." "Experience must be our only guide; reason may mislead us." "Instagram is Twitter for people who can't read."
