If he was on the steps of the TSBD then he was surrounded by people, by his fellow co-workers like Frazier and others. They can give him an alibi. There's no need to take off. But I thought you believed he was inside having lunch? He said in a brief interview that he was inside the building at the time of the shooting.
Again: the people who were there, around the steps, didn't know exactly what happened. It was chaos and confusion. Nobody knew what happened. Those who were there said they asked each other about what was going on. In fact, a number of people ran to the Grassy Knoll, fence and overpass. That's where some people thought the shots came from.
Oswald did numerous things after the shooting that I simply don't think an innocent person would have done. In fact, he did things that a guilty person would do. But others, like you, obviously disagree.
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There were not many Oswald coworkers to give him alibi being on the TSBD front steps, two or three, not more... Shelley, Lovelady, Fraizer... He was standing at the back row and everybodys attention was forward. In addition, he might went out minute before motorcade arrived. Now, If you look on how DPD handled Oswald, dragging and pulling him back and forward, if you look Ruby killing him, if you look crowd celebrating his murder, if you are 19 years old in a community hating communists (as Oswald was presented at the very start)... if you take everything into the consideration, will YOU ONLY step up and say he was on the steps? No, sir, you would not have courage same as Frazier never did, nobody would have courage for sure. Fraizer is still alive and I think that one day he will say it but who knows.
People did not know what was going on because of a simple reason: there were NO three gun shots but three sounds. You can search Youtube for videos of people reacting on shooting and gun shoots. Reaction is dunk, run away and hide. If the shots came from the TSBD sixth floor, many, many would dunk, run away and hide but almost nobody did. Instead you have only people next to the limo at Zapruder frame 313 who reacted as people react on shooting. This made you to conclude that shots came from the limo area...
It is true that Oswald did some things that a guilty person would do but that does not makes him guilty, right? Lets say you have illegal gun and you walk down the street and see a murder. What would you do? You know you are not guilty but you still have a gun with you. Will you keep it or throw it away?If you keep it and police finds it, they will interrogate you, maybe make you a suspect. So, you will get rid of it for sure as soon as possible, right? Same as Oswald, leaving TSBD right away, does not make him guilty, having a gun also, resisting a rest also does not make him guilty. Does leaving a wedding ring makes him guilty!? Absolutely not.