Most of the relevant evidence was known within 48 hours. It all pointed to Oswald just as it does nearly six decades later. Any reasonable person would conclude from the evidence that Oswald was assassin. What they didn't want to happen is to be hijacked into WWIII by those who saw a Russians or Cuban conspiracy behind the assassination when there was no credible evidence of such.
In other words; they ruled out a conspiracy from day two after not having investigated any possible conspiracy and thus not finding any evidence of such....
So, you agree that Oswald was determined, in less than two days, to be a lone gun man based on no evidence whatsoever.