You also have seen the film of many more people running up the grassy knoll or am I confusing that with a film of NO people running up the street to a building that deals with school books or something???
Here is a photo not long after the assassination, where did the running people come from?
A little bit later we see a cop running towards the railway overpass but we still see NO one running up the knoll, where are they?
The motorbike cop we saw running towards the railway was followed by the first witnesses and this is NO where near the popular grassy knoll assassin positions?
Here is more people starting to gather, some seem to be moving towards the cop at the railway overpass and still NO one is running up the Knoll steps, where did they come from?
So in conclusion it's obvious that people moved to this end of Elm street because this is where the President was shot and the people who were later running up the steps were not initially that close.
JohnM