Jack Ruby did NOT got to the garage with the intention of shooting Oswald, and we know that beyond the slightest shadow of a doubt, because:
1) he brought his dog along
2) he showed up an hour and twenty minutes late
He had to know that if he shot Oswald in a police garage, crowded with police, that the police would arrest him on the spot, and he would never go home. So, why bring the dog? He wouldn't. He couldn't. But, that's only if he was planning to shoot Oswald. If he wasn't going to shoot Oswald, then he brought the dog because he had every expectation of driving home with her.
And likewise, it was widely publicized that Oswald would be moved at 10 that morning. So, if Ruby were going to shoot Oswald, he would have showed up somewhat before 10. He certainly would not have come an hour and twenty minutes after 10.
So, there really is NO CHANCE that Ruby went there to shoot Oswald. So, why did he go there? HE DIDN'T KNOW. He honestly didn't know. The only reason he ever gave for walking to the ramp is that the mob of people there attracted him, raised his curiosity. But, as I explained last night, they had no reason to be there. Oswald was NOT going to be brought out that way. He was going to be brought out on Commerce Street, where the Brinks trunk was in the driveway. Those people waiting on Main Street had no reason to be there at all. So, why were they were? They were Ops. They were there for Ruby. He may have been specifically programmed to look for the crowd of people and go to them. And once he got to them, who knows, one or more of them may have coaxed him down the ramp.
But, Ruby didn't know why he walked down the ramp. He never gave a reason for that, which is to say, he did not have a reason; he did it for no reason. He did it because he was programmed to do it; brainwashed to do it; hypnotized to do it. And that's why he did it. It's the only reason why he did it.