Several people have made the point this was a Senate hearing, and not a trial. That being the case, the scope of inquiry is far broader, and issues like relevance do not mean much. The whole point of many of these hearings (aside from allowing Senators to grandstand) is to ferret out information about a panpoly of things. These hearings were about "the mafia" with Michael Corleone as the big fish. So why they would have Tom on their poster, and do nothing to besmirch him remains curious.