I don't have a clear answer for you,but if I had to speculate,I would pick Gambino as the one most likely to have been a hitter. He was made in Sicily when he was nineteen. As we know,the Sicilian Mob was totally ruthless,and would kill babies in their cribs if it was necessary to satisfy a vendetta.For them to make a guy that young tells me that he had a notch or two on his gun. In addition,a duplicitous,cunning weasel like Gambino knew that killing would have been a step up in his world,so I could see him doing whatever he had to do.