Perhaps Vito's sending Luca was a tipoff as someone has pointed out. Just how much did that action influence Barzini's and Sollozzo's decision to murder Vito? That, in turn, calls into question how much a role Sonny's outburst influenced them.
"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."