That is always the reason the Warren Commission apologists give against a conspiracy. That people are such blabbermouths that they cannot keep a secret. If that were true then how do we have a CIA? Or for that matter, how does any country in the world maintain their clandestine services?
There were about a dozen people involved in the Lincoln assassination conspiracy. How many of those talked? How about none? That is right—not a single one of them did. Of course Booth was clever. He found ways to incriminate and compromise all around him, with public meetings at hotels, requiring fellow plotters to rent the same horse at the stable as he did (which leaves a written record), or saving letters from associates who were dumb enough to answer Booth’s questions regarding the conspiracy, which he would then keep in his sister’s safe. Booth would then let them know that if he hanged so would they.
The MyLai massacre has parallels too. Physiologist and author M. Scott Peck mentioned in his book People of the Lie, that almost 500 military personal knew about the slaughter but none talked. As Dr. Peck discovered, none of these men talked because they felt they had done nothing wrong. Hence, no need to discuss the issue. The incident slowly emerged after two men who were not involved wrote their congressmen.
John Stringer, chief medical photographer a Bethesda, told the Assassination Records Review Board questioners, under oath, that the morning after the autopsy he and others were taken into a room, read the riot act by a naval officer, and told to sign a nondisclosure agreement. Did any of those people talk? Not a one till Stringer was allowed to give his testimony for the ARRB in the mid 1990s.
People are good at keeping secrets when it counts. The idea that secrets can’t be kept is a red herring. Who ever heard of the National Reconnaissance Office until we were finally told in the early 1990’s? Who leaked it? No one. And think of all the people that worked in that department. The same is true for the Manhattan Project during World War Two. Hundreds worked on the atomic bomb project and the secret was never leaked. Here, the importance of the effort and the appeal to the natural patriotic fervor of the time.
So people can be kept quiet. Compromise, blackmail, forced signing of release forms, appeal to patriotism, and intimidation through death threats and other means all have their place. Most uncommon is M. Scott Peck’s discovery that if a person feels he has not done anything wrong, there is no need to discuss it. If your boss orders you to a task, and your boss is not immoral, you think nothing of it and do as you are told. A natural inhibitor for creating silence is created. It can be seen, at least incidentally, in the behaviors of those first responders to the assassination.
Of course the man at the center of the storm kept his silence too.
Sources: McKnight, Gerald, Breach of Trust; Kauffman, Michael, American Brutus; various documents, MaryFerrell.org; Peck, M. Scott, People of the Lie; Google