That's right it was part of his agreement with the feds. There was a limit on the amount of years he would have to spend as a witness and he also wouldn't have to testify against his old crew. I'm sure they allowed him those conditions because he would help give them the dirt on Gotti plus all the other information he could provide.

Interestingly, he also refused to testify against Gaspipe Casso. Not because of loyalty, but because he was scared of what Casso might do.