Well, Martin (Fox, not Sock Guy), welcome to the club. As you can see, you are in a wonderland of folks who seem to have difficulty grasping the point you are making or staying on topic for more than two posts.
As I understood it, your premise ("for the sake of argument," as we lawyers say) is that Oswald was not the shooter. If this were true, we are faced with the difficulty (among many others) of how the actual shooter exited the TSBD.
For the sake of argument - even though I think Oswald was the actual shooter - my guess would be that actual shooter would have been nicely dressed, passable as a visitor to one of the publishing companies, a detective or even a police officer, and would've simply blended in for a bit until he could've safely exited the TSBD. I wouldn't picture some "fleeing felon" scenario that would have drawn attention to him.
I don't think this really works, for all the reasons set forth in my own thread "Try thinking about the TSBD" (below), but this would be my best guess if there actually was a shooter other than Oswald inside the TSBD.
https://www.jfkassassinationforum.com/index.php/topic,4230.0.html