Oswald's rifle was found on the 6th floor, fired bullet casings from his rifle were found by the window, witnesses did see a rifle pointed from that window at the moment of the assassination (i.e. 12:30).
Oswald's rifle was found on the 6th floor, Ok Granted..... WHEN was it hidden beneath the pallet ??
When seems obvious. As Oswald boogied for the stairs to get off the floor. Oswald's rifle was on the floor from which a shooter assassinated JFK with a rifle at 12:30. Fired bullet casings from Oswald's rifle were found by the window from which witnesses confirm they saw a rifle at the moment of the assassination. That rifle was found hidden on the 6th floor. Oswald fled the scene down the stairs near the location where the rifle was left. We don't have to consult Sherlock Holmes here to connect the dots.
As a bonus, I'll give you actual speculation and excite Martin to take us down the rabbit hole. After Oswald learned of the motorcade route sometime that week, he scouted the TSBD for a location that afford the best combination of shooting location and seclusion to commit the act. The 6th floor window was ideal due to the boxes surrounding that window, view down Elm, and it was out of sight of the elevator/stairs. He might have had an alternative if it that turned out to not be feasible for some reason on the day of the assassination. Maybe on the 7th floor. Once he picks a shooting location, he decides on a good place to hide the rifle on that floor. He creates or finds such a place on the 6th floor sometime that week. When he brings his bag/rifle to work on 11.22 he heads directly to that location and stashes the rifle. He can retrieve it on the floor from which he intends to commit the act. He walks around with his clipboard on the 6th floor after noon giving him the appearance of having a job-related purpose for being there should he encounter anyone on the floor. At some point after noon, likely before BRW arrives on the floor, he puts his clipboard down and retrieves the bag. The location of the clipboard, therefore, provides some insight as to where he hid the rifle that morning. He carries the bag to the SN, takes out the rifle, and does whatever assembly is required while he waits. After the shooting, he stashes the rifle in the same place he hid it that morning. Not taking him more than a few seconds.
