From what I've heard there isn't much doubt it was Tony Pro and I've also heard Sheerin's book is pretty credible.
Apparently they did not want Hoffa to run for president of the Teamsters again because they had a good thing going with Frank Fritzsimmons running it, but Hoffa was going to run again anyway.
The Hoffa stuff in the book sounds plausible but he also claims to have killed Joe Gallo which makes me question the whole thing.
