Do you realize how HIGH above the floor of the Pergola Shelter that window is?
scaffolding | ˈskafəldiNG, ˈskaˌfōldiNG |nouna temporary structure on the outside or inside of a building, made usually of wooden planks and metal poles, used by workers while building, repairing, or cleaning the building: two of the shops had scaffolding against them | [as modifier] : scaffolding poles.
Are you saying a shooter brought Planks and/or Poles into the Shelter and assembled a scaffold? Then disassembled the Planks/Poles and removed them from the Shelter? All without being seen/heard? Zapruder and Sitzman were inside that same shelter about 1 minute after the Kill Shot.
What are you getting at?