Colombo was a walking target who fell in love with own bullshit; with EVERY reason in the world to have him hit, logic says it was the Commission, not Gallo, who had other issues to deal with then.

That said, who the fuck was Jerome Johnson, really, and how the hell did someone coerce/convince him into taking that job? Crazy is easy to find, competent isn't so you gotta wonder what he got (partial payment beforehand?) & what he ** thought ** he was getting into. Even if Colombos bodyguards didn't kill Johnson first, what chance was there he could make a getaway from that crowd & cops on the scene?