Here's my 'basic understanding' of this particular fact: You lot yet have to prove that anyone other than the shooter(s) knew there was to be an attempt made on Kennedy that day.
Milteer knew this was in the making, and Walker knew too, that's why he took the flight for his alibi, he set up the shooting on himself in a similar fashion as part of this alibi, and it also played a part in framing the patsy.
The military who were dealing in WW2 weapons had people in Kleins as well, to manipulate pieces of paper work, is a piece of cake, bottom line is Oswald had no clue what happened on the day.