When murder machine came out in 1990 I beleive Casso hadn't flipped yet. So there was only speculation that Nino did it, but than Casso flipped in '94 and revealed it was the twins who did it at patty testas house. Casso wasn't a good witness as we have all come to see so but their really isn't a reason for him to lie with this, so most everyone buys the story the he gave.