Virtually every critic of the Warren Commission and writer of conspiracy books ignores the requirement for an alternative 6th floor shooter. If not Oswald, someone who used Oswald's rifle to assassinate President Kennedy.
There was a 6th floor TSBD shooter -- Oswald or a hit-man. He would have had the same difficulties that Oswald did in escaping the crime scene.
For all claims of "impossibility" for Oswald being the assassin, the real 6th floor shooter is equally affected.
Officer Marion Baker (accompanied by Mr. Truly) went up the back stairs of the TSBD a little more than a minute after the shots were fired. Baker found Oswald in the 2nd floor lunch room. Reconstructions have demonstrated that its possible to get from the 6th floor sniper's nest to the 2nd floor lunch room in less than 90 seconds. Even if this is disputed by conspiracy theorists, a similar time frame exists for the real 6th floor shooter. How did he get past Baker and Truly on the stairwell and escape the TSBD? If there truly was a conspiracy: The plotters would require a foolproof plan in which their shooter could escape from the crime scene without being captured or even seen by a witness.
There would need to be accomplices who would prevent employees being inside the TSBD before, during and after the time of the assassination. Every floor up to the 6th (and even the 7th) would be off limits to everyone except the shooter and his helpers plus Oswald. This did not happen.
An innocent Oswald would need to be restrained prior to and during the assassination. It did not happen because Oswald never explained this to his interrogators and never "blabbed" this scenario to the press (in front of cameras and microphones) at City Hall.
No professional hit-man would accept a contract to assassinate President Kennedy. The chance of committing the crime and avoiding capture is so slight that no amount of money would be worth the risk.
An inside job is far more plausible. Oswald had the advantage of legitimately being anywhere in the TSBD after the assassination. That's why Officer Baker let Oswald go due to Truly vouching for his employee. Officer Baker would have arrested the real 6th floor shooter.
Way too many assumptions as a starting point.
It assumes the rifle found at the TSBD belonged to Oswald and that shots were indeed fired from the 6th floor.
It also assumes that another killer would have needed to come down the stairs that Baker and Truly were on.
It assumes that no professional hit-man would accept a contract to assassinate President Kennedy.
And it assumes that Baker would have seen the real shooter on the 6th floor.
With all these assumptions the entire thing has become an insignificant hypothetical scenario with a pre-determined conclusion build in.
And worst of all, it completely ignores other possibilities like this one; even if we assume Kennedy's killer did shoot from the 6th floor. Why would he do the obvious and instantly flee the building, when he also can hide and mingle with the crowd that he could reasonably assume would invade the building. All he needed to do is dress like a police officer, have a fake or perhaps even a real badge and act like a cop. With so many people around who did not belong in the building he would not stand out. All he needed to do is make his way down the stairs when the cops are upstairs and simply walk out of the building.
Now, you tell, as I am sure you will, why such a scenario wouldn't work?