it was never really made clear what relationship gallo had with black gangsters after he was released. One informant did state that colombos house was being staked out by some black guys in a car and that colombo believed it was gallo trying to intimidate him. i think that gallo was the more likely culprit behind his killing, whether he got permission or not from gambino i dont know. The black guy they used was apparantly a hardcore criminal himself that would do things for a price.

Another theory ive seen a few times was that johnson may have been avenging the deaths of his friend and the guys girlfriend when they were killed by some colombo guys at a party where they were working as waiters. It would explain why he would take such a huge risk of getting caught or killed.