Costello himself allowed being filmed, but at the last moment he changed his mind a asked not to film his face. Not so smart because it seemed like he had something to hide. He didnt do so well when he was interrogated. A year earlier he also testified for a committee and that time he did great. He was known as the 'prime minister' of New York because he knew so many important people and had so much influence. Kefauver changed all that, politicians and bussinessmen got scared of being seen with Costello.

The Kefauver hearings also meant the end for Willie Moretti, the guy that launched Sinatra.He ran a big piece of New Yersey for the Genovese-family. And was a close friend of Costello. He even had a seat on the national commission. But after testifying (he was the only one) he got killed.

Word is that he got senile and that why they killed him.
But this could be a mob-excuse.