They did not need Massino, they had him convicted and still gave him one of the best deals ever. They would LOVE to have Bascaino, it must eat away at them that they could not get him to rat. That is why they made his sentence so severe. They willl take any rat, they even took Casso, until his testimony contradicted with another's. They took Gravano, even eater he told them he killed 20 people. It's an ego thing to the FBI and prosecutors, Bascaino could get out any time he wants by cooperating, but he's a man and not a rat.