He was under immunity and testified against Cerone and others in a gambling case. He faced imprisonment for contempt if he did not take the stand. He was not in very good health so taking the fifth like Sam Giancana and serving a year was not a viable option for him. With that said, even after taking the stand he did his best to avoid questions and presenter many of his answers in half truths, so it wasn't like he took the stand and spilled his guts.