The most likely person was Joey Gallo. He was still unhappy about the setup of the crime family after he returned from prison. Carlo Gambino rumored to being involved in the Joe Colombo hit has been around before Selwyn Raab put it in is book. Colombo was the founder of the Italian-American Civil Rights League, and charged store owners for placing his stickers in their stores. If there was a conspiracy in the Colombo hit, then other members should be mentioned, at the top of my head the three members who had sitdowns or had others sit down with Colombo in their place were Natale "Joe Diamonds" Evola of the Bonannos, Vincenzo "Vinny" Rao and Vincent Foceri of the Luccheses, Thomas DiBella and a few of the other Capos of the Colombos who went through Joseph "Joey Yack" Yacovelli about their complaints. These sitdowns happened a lot from 1970 till the Colombo shooting, the stickers seems to be the big issue with these sitdowns, weather Colombo was not sharing in the profits or he was forcing the personal family members of these other crime families to pay to place the sticker in their shops is not known. One thing that is known is that Joey Gallo had the motive, opertunity and the means to carry out the Colombo hit, as well as the crime families felt Gallo was behind the hit.