J. Edgar Hoover: "Need To Convince Public That Oswald Is Real Assassin"

In a memo issued by Hoover, he appeared to be particularly concerned that the public would have to be compelled to believe that Oswald was a lone actor - not part of a larger conspiracy.

"There is nothing further on the Oswald case except that he is dead."

In the 1964 Warren Report on Kennedy's assassination, NBC notes, Hoover was firm in stating that he hadn't seen "any scintilla of evidence" suggesting a conspiracy - a sentiment he expressed in other public forums, as well, but not in words as blunt as those he used the day Oswald was killed.
Referring to Nicholas Katzenbach, the deputy attorney general at the time, Hoover dictated:

"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."

             "There is nothing further on the Seth Rich case except that he is dead."