Very interesting post.
We can basically only speculate who was behind the Colombo downfall. It is frustrating that no one has managed to even come close to an explanation. (Don´t get me wrong. I mean the investigators back then...)
The strange thing is that neither one of the many informants the FBI, for example, had disposal of had something valuable to offer.
Sure, there has been talk of Gambino and the Gallos and there has been talk of conspiracies that points to the U.S. government. And as usual, when a case of this kind can not be resolved, somebody always mentions the "lonly madman" as the only perpetrator. But that´s to take the easy way out, isn´t it?
In my opinion, Carmine Persico had most to gain from a Colombo rubb out. Although he was imprisoned when it happened, he may have had a hand in it all. Of course, the ultimate was to get people to believe it was the Gallos. In this way, I think, Persico managed to kill two birds with one stone.
Also keep in mind that Colombo had betrayed his boss Magliocco by revealing his plans regarding the executions of Gambino and Lucchese before the Commission. When Colombo was appointed boss many high-ranking members, who previously had positions of power within the family and had been very close to both Magliocco and Profaci (some were relatives of them), were demoted to the rank of soldiers. In their world, and in their mindset, being demoted from a top guy to bottom of a barrel is devastating powerwise.
What if the murder attempt on Colombo was a revenge for his betrayal and a result of his restructure back in 1963/1964?