After the death of Trafficante his lawyer described carrying a message to him and Marcello from Hoffa. It was the JFK should be killed. When the message was given them he said that they looked at each other with a look that meant they took it seriously and was no joke.
After it was done Marcello said Hoffa owed him BIG TIME.
I worked (indirectly) for the Giacalone family of Detroit in the late 1970’s. After Hoffa disappeared, the FBI came to our facility (which will remain nameless) and interviewed us about this, that and the other. Hoffa was a clear enemy of the Kennedy brothers and he knew it all, so, he HAD to disappear and he did.