It was changed at the last moment. Why? The trip was nearing its end, and the car should have been picking up speed on Dealy Plaza. But with the new ride the procession must take Houston Street and Elm Street with a sharp bend that forces the driver to slow down to 16 km/h. The normal speed being more like 40km/h.
The fifth-floor window of the book depository gives a direct view of Houston Street. So why not shoot with Kennedy in front of you, rather than from behind and further away ? As if that wasn't enough, a tree should have obstructed the view of the shot. FBI Director Hoover joked that "leaves fall in November". But it's a Texas oak, and its leaves fall in March. However, this window sould never been opened. A huge security vulnerability is to be deplored. Under normal circumstances, no window would have been opened, no one would have had a newspaper under their arm or opened an umbrella. Officers would have been posted on every roof and around the car. None of this was done.
3 shots in 6 seconds. It takes between 2 and 3 seconds to reload between each shot. The maths is done, it's almost impossible for Oswald to have fired all three shots. Especially as experts have tried to recreate the feat, without success. What's more, his former comrades in the navy don't rate him as a good shot. The clock is started : Oswald fires his 3 bullets, leaves three shells, cleans his prints from the gun, hides it at the other end of the room, goes down 4 floors, passing two employees who wouldn't have seen him and arrives fresh (not out of breath) on the 1st floor at the canteen just as a policeman arrives to find out who he is. All in 90 seconds. He doesn't hurry out of the building, but buys himself a Coke from the vending machine, passes an employee without hurrying and exits through the main door, which is further away, where the police are gathered. Although the officers were sure that the shots were coming from the book depository, it was not cordoned off until 10 minutes later.
To commit the second murder of police officer Tippit, Oswald would have had to run 1.5km in 6 to 11 minutes. Another strange element is the witnesses to this murder. The closest one does not recognise Oswald, so they refuse to bring him to the commission. Another witness said she had seen two men who then split in two directions, but she was not invited to the identification.