Chief Justice Earl Warren

"...Warren continued by saying that Johnson then called him in personally. The president said he was greatly disturbed by the rumors going around the world about a conspiracy, perhaps involving Castro or the Russians. 

And that if these continued to grow, it could catapult the world into a nuclear war. Johnson then told Warren that he had just talked to Secretary of Defense Bob McNamara, and if such a thing occurred, a first strike by the Soviets would cost the USA as many as sixty million lives. 

“Now, I don’t want Mr. Khrushchev to be told tomorrow and be testifying before a camera that he killed this fellow…and that Castro killed him.” Johnson then confirmed that Warren did start to weep.

“…we’ve got to take this out of the arena where they’re testifying that Khrushchev and Castro did this and did that and check us into a war that can kill 40 million Americans in an hour….”

The important point to note here is the material Johnson used to seal the deal with Warren. Clearly, this was the information about Oswald’s visits to the Russian and Cuban consulates in Mexico City and his alleged talk with Valery Kostikov at the Soviet consulate. 

Kostikov would be revealed to be a secret KGB agent in charge of assassinations in the Western Hemisphere.

Warren left the meeting so emotionally distraught that he had tears in his eyes."