Here is a not-to-be-missed web page from the U.S. federal government addressing various conspiracy theories that involve the U.S. government:
Conspiracy Theories and Misinformation.
They write: “Conspiracy theories exist in the realm of myth, where imaginations run wild, fears trump facts, and evidence is ignored. As a superpower, the United States is often cast as a villain in these dramas.”
Here's a warning from the federal government website:
Perhaps more conspiracy theories surround Lee Harvey Oswald, who assassinated President John Kennedy in 1963, than anyone in American history. The Soviet KGB, Cuba, the mafia, the CIA, Lyndon Johnson and others have been blamed for killing Kennedy, but all evidence indicates that Oswald acted alone.