A contingency plan for what here? What are you suggesting happened that caused them to change the plan? That is not an explanation for the sequence of events. There isn't any rational narrative for these POWERFUL people planting Oswald's wallet at the crime scene (great evidence to link him to the Tippit murder) to suppress it in favor of Oswald's arrest wallet. Your fantasy conspirators would have known that it was likely that Oswald would have a wallet on him when arrested or killed that day. So any plan that entails leaving a wallet at the Tippit scene must incorporate the likelihood of a second wallet being on Oswald's person upon his arrest/death and plan to suppress that wallet. And imagine the plan of actually leaving a wallet at the Tippit scene, allowing it to be discovered, but then suppressing it. LOL. That makes no sense as a contingency plan or otherwise. It is extremely risky and pointless. If the plan was to frame Oswald for this crime, then all the incentives are to claim that Oswald's wallet was found at the Tippit scene. Instead what is being suggested is that conspirators behind Oswald's frame up suppressed great evidence of his guilt! It just doesn't add up that whoever discovered the wallet would not have radioed in the identity of the suspect and that this valuable evidence of Oswald's guilt would for some inexplicable reason then be covered up by the very folks who otherwise are alleged to be framing him. It's a hodgepodge of nonsense.
So I must theorize? How about you comment on what is seemingly a fact, a picture with Oswald's wallet in Westbrook's hand, witness testimony etc. What would it be in the order of things that I need to comment on what exactly went wrong with a plan I have knowledge. It opens the land of pure conjecture and it seems to your favorite form of fantasy land
I kind of changed my mind and will offer a scenario That being said I am familiar with those who insist on taking to frames of examination such as yours Critics of a particular theory must provide the correct version of all events at the same time Anyway you want a shot at it, I will give you one Lets say the conspirators wanted to frame Oswald, and it was important to them to either capture him or kill him shortly after the assassination Therefore you would want a contingent reason to take him into custody, so you create the circumstances with the Tippit murder until you have him in custody Then once you have him in custody, it may look better to not use the wallet evidence because lets face it it looks a little suspicious for the suspect to seemingly leave his wallet at the scene