A - 7 : Alphonse "Little Al" D'Arco (Lucchese)

Little piece of triva for you. When Casso wanted to kill Lucchese made guy Bruno Facciolo, he said that he was a rat and he knew it because his cop friends told him that a Lucchese soldier was an informant and, in one of his report, this informant used the nickname "Little Al" to refer to D'arco.

Apparently, Bruno Facciolo was the only guy in the Family who call D'Arco "Little Al" therefore he was the prime suspect.

That's the official story. The unofficial one is that Bruno Facciolo had a lot of guys around him and he was an influential figure in the Family. Casso feared he had enough power to make a move against him so he had him killed portraying him as an informant, like he did with all his potential rivals.