LONDON — Twenty-five minutes before John F. Kennedy was assassinated, a British newspaper received an anonymous tip about "some big news" in the United States, according to the trove of more than 2,800 documents released late Thursday by the National Archives.

The mystery call was made to a senior reporter at the Cambridge News, a paper that serves the East Anglia area of eastern England, on Nov. 22, 1963, at 6:05 p.m. local time. Kennedy was shot shortly afterward, as he rode in a presidential motorcade in Dallas, Texas, at 12:30 p.m. CST. Dallas is six hours behind Britain.

"The caller said only that the Cambridge News reporter should call the American Embassy in London for some big news and then hung up," the memo from the CIA's James Angleton to FBI director J. Edgar Hoover said.

The revelation, one of many that emerged from the planned release of the Kennedy assassination documents — so far, there's no smoking guns — adds to the raft of conspiracy theories surrounding his death. In fact, the memo was first released in July, but went unreported until the cache of files was released Thursday.

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The memo, dated Nov. 26, 1963, says: "After the word of the President's death was received the reporter informed the Cambridge police of the anonymous call, and the police informed MI5. The important point is that the call was made, according to MI5 calculations, about 25 minutes before the President was shot. The Cambridge reporter had never received a call of this kind before, and MI5 state that he is known to them as a sound and loyal person with no security record."

MI5 is Britain's domestic security agency.

The reporter's name was not mentioned in the memo, which adds that MI5 had received "similar anonymous phone calls of a strangely coincidental nature."

The Cambridge News noted in a story Friday that it too did not know the name of the reporter who took the call, although it said the existence of the memo was first discovered by a lawyer, Michael Eddowes, who devoted much of his life to investigating the mystery surrounding Kennedy's death.

Eddowes, who died in 1992, told the Cambridge News in 1981 that he believed the anonymous caller was a British-born Soviet agent named Albert Osborne.

Two months before Kennedy's assassination, Eddowes believed that Osborne, who also apparently used the alias John Howard Bowen, had befriended Lee Harvey Oswald, the man ultimately charged with murdering Kennedy.

Eddowes' theory was that the call was made "because the Soviet Union was eager that the assassination should be seen as a conspiracy," according to the paper. It was not clear why the Cambridge News was specifically chosen, or why the call was made to a local paper as opposed to national one, which may have led to greater exposure.

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