New York Times article from 1976, when Howard K. Smith reported what LBJ had said in 1968. My guess is that LBJ actually knew no more than yours truly, possibly considerably less.
Lyndon B. Johnson privately linked Premier Fidel Castro of Cuba to the assassination of President John F. Kennedy, Howard K. Smith, the ABC News commentator, said last night, quoting from what he called a “confidential” convexsation with President Johnson in his tenure in the White House.
“Mr. Johnson often dealt in blarney; and what he told me may have been that,” Mr. Smith said, in reporting the conversation.
“I'll tell you something [about Kennedy's murder) that will rock you,” Mr. Smith quoted the late President as saying. “Then he said, Kennedy was trying to get to Castro, but Castro got to him first,” Mr. Smith continued.
“I was rocked all right, begged for details,” Mr. Smith added. “He refused, saying it will all come out one day."
Mr. Smith, who based his report on “thorough notes,” written an hour after the conversation, said he was making the conversation public because the issue of the assassination had been “revived, responsibly, by Senators.”
As “evidence that belief in Cuban assassination plots was alive in Washington,” during Mr. Johnson's first months in office, Mr. Smith said that Mr. Johnson's airplane had once been diverted from Miami to an obscure rural airport because of a rumor that “a Cuban kamikaze pilot had been ordered to ram his plane.”
Those dang Cuban kamikaze pilots, they're the worst.