Oswald wasn't properly searched until they finally searched him and found the bus transfer in the shirt pocket and five live bullets in his left front pants pocket.
It's hard to fathom the logic behind suggesting that a short delay in finding the bus transfer after his arrest lends itself somehow to it being planted. But again, this implies that Oswald never got on the bus, and someone is trying to place Oswald there by planting evidence. We are left in a sense of wonderment, however, as to WHY they are doing this. In this CTer fantasy, the DPD or someone goes to the considerable risk of planting evidence in a homicide case - and not just any homicide case but the assassination of the president. WHY is it so important for them to place Oswald on this bus that goes nowhere? How do they ensure that the driver and other passengers either support or at least don't refute that Oswald got on that bus? How do they know that Oswald was not in the presence of someone else who could vouch for him at the time he was supposed to be on the bus? None of that is ever addressed. It's just the transfer wasn't found right away, so that makes it suspect for some unspecified reason.