Denis, maybe if Ruby had a more sophisticated weapon it might throw suspicion on the whole thing, who knows what they were thinking. Why did Ruby say what he said about taking what information he had to his grave. That in itself says he knows a lot more than he saying. Ruby had no love for JFK, the mob hated RFK and JFK. Again, Ruby’s club was owned by Dallas mob which was under the thumb of Marcello.
I agree with you there should have been someone else to take out Oswald earlier, like your idea, a corrupt cop. I can’t explain why they didn’t.