There were probably quite a few people that probably wanted the Musitano's out of the way.

-The Papalia's or members of the clan, may have wanted to revenge.
-The Luppino's would benefit;also if Ken Murdock is to be believed there was a plot by the Musitano's to have the Luppino's killed. Musitano's were emboldened by their close ties to Rizzuto's.
-The Violi's for that same reason, their close ties to the Rizzuto.

Can anybody else come up with other possible theories?