They certainly knew Fanucci was killed--he stopped collecting from them, and no doubt the police found his body and a crowd saw it taken away. When Vito showed up and started "protecting" the businesses that Fanucci had "protected" previously, they put two and two together.
Ntra la porta tua lu sangu � sparsu,
E nun me mporta si ce muoru accisu...
E s'iddu muoru e vaju mparadisu
Si nun ce truovo a ttia, mancu ce trasu.
| 
