This remains one of the most intruiging topics of the films. Because they were immediately recognised by Rocco to be from New York, it might very well be that they were from the same family, possibly the Rosato faction. It appears that Roth's and Johnny Ola's men were stationed in Florida, so that rules out that they were from Ola's crew, which wouldn't have been a smart move as that would have immediately put the blame on them. Perhaps it were assassins that Roth knew from his Murder Inc. days, considering that Moe Greene was a Murder Inc. hitman and Roth's protégé.