Sonny Black definitely died as a result of Brasco. And he went to his death knowing it. After he'd nominated Pistone for induction into the Bonanno's, he began taking him around, meeting others and introducing him as a "friend of ours". Which was a big no-no, especially when it was revealed he was a fed. That's the reason his hands were cut off after they killed him. This was confirmed during Massino's trial in '03. He was killed 17 days after the agents showed up to The Motion Lounge and showed him the pictures of Pistone in uniform. His girlfriend had even called Pistone, according to him, when Napilitano was declared missing.