Another clue that it was Barzini al along was the deal they floated out to the Corleones after the two atempts on Vit's life failed. Sonny kills Bruno Tattaglia, and they offer to cancel it out very readily. I don't know that Tattaglia would be that forgiving about his own son, but Barzini....
That's a good point, dt. It was pretty grand of them to say that Bruno Tattaglia's death is tit-for-tat for Vito's shooting. Couldn't have been Tat's sentiment.
Contrast it with the movie's opening scene. Bonasera wants Vito to kill the two boys who ruined his daughter. "I ask you for justice," pleads Bonasera. "That is not justice," Vito replies. "Your daughter is still alive." Well, Vito was still alive after the shooting, but Bruno was dead.