You keep assuming that a conspiracy is necessarily a "large secret conspiracy". A conspiracy could be two people.
But the conspiracy that CTers really mean is not a conspiracy of two people but a much large conspiracy.
The CIA was in on it.
But the FBI investigated it and found the evidence went against Oswald. That?s not problem, the FBI was in on it.
But the Dallas Police Department collected the rifle, a handgun (wrestled out of Oswald?s hand), shells, statements by Oswald showing he lied about owning a rifle and bringing a long bag to work and other evidence. But that?s no problem because the Dallas Police Department was in on it.
But the autopsy shows all the shots came from behind. But that?s no problem because the autopsy doctors were in on it.
If CTers want me to believe that they believe in a small conspiracy, they need to tell me what evidence is real and what is faked. And how many people would be needed to make it fake. How many FBI agents. How many Dallas Policemen. And how the conspiracy arranged that always one of the conspirators would evaluate the evidence and prevent an honest investigator from being brought in.