I'm not sure anyone in the US government is concerned about the lives of people in Russia or Cuba who might have been connected to Oswald or JFK's assassination in any way.
The most likely concern to explain all the secrecy is to protect the reputation of prominent families here, or the reputation of the agencies who pulled off a coup and pinned it on Oswald.
When the top law enforcement official dictates a memo THE DAY AFTER the assassination, that says:
(On November 23, 1963) "The thing I am concerned about, and so is Mr. Katzenbach, is having something issued so we can convince the public that Oswald is the real assassin." - J. Edgar Hoover
THE DAY AFTER!
If that doesn't concern you... Whew!... I'm not sure any rational conversation about this can be productive... and I wouldn't suspect you to accept a conspiracy at the top level if MORE evidence is produced to implicate the guilty parties.
Did I say, THE DAY AFTER!?
Yes, THE DAY AFTER!
Hoover had no concern to discover the truth of the matter. A rush to judgment and a rush to pin it all on Oswald.
If that doesn't concern you and make you want to investigate Hoover and others at the top level of government, you have little or no concern for truth and justice... and no concern for the principle of "innocent, until proven guilty."
There's your evidence of conspiracy, if you choose to accept it.