My sense of this is that you can use the template of "Oswald" allowing himself to be set-up at the Book Depository as part of his covert duties to this shooting and all the evidence for it...Oswald was CIA so he was doing what CIA told him to do and helping set himself up...Lone Nutters and the Warren Commission take advantage of this by citing it straight as if it were just straight evidence instead of acknowledging this context...It is awfully easy to set someone up who is helping you set himself up...Just like "Oswald" never took a shot at the Depository he probably never took a shot at Walker either...
If you think about it, if the note had Oswald's hand-writing then it was probably written before the assassination...Which would mean it probably wasn't forged after the assassination...
If the Carcano was delivered March 25th then "Oswald" should have had the bullets for it...The steel-jacketed bullet found at the Walker shooting scene was almost certainly not fired from the odd-caliber 6.5mm Carcano...It would make sense that "Oswald" would have gotten the bullets for the rifle he just allegedly bought near the time he bought the gun...Especially if he intended to make political use of it shortly after buying it...So therefore it would be unlikely a copper-jacketed round would not have been used...
My view is that the decision to kill Kennedy had been made by the plotters and "Oswald" was cooperating with a whole new set of plans for his undercover work...They were taking it to the next level...It is possible the plotters were conditioning "Oswald" in to allowing himself to be used as a patsy made to look like a crazed communist-sympathizer Lone Gunman...It is under this context that it would be possible for "Oswald" to both write the note and not have shot at Walker...The premise being that Oswald's own admission in writing that he was going deep on a possible suicide mission could be used as evidence of a similar event with Kennedy...The plotters did not have "Oswald" write a similar note for the 22nd because they did not want to scare "Oswald" in to caution...