Newly released files about John F Kennedy’s assassination dismiss theories that shooter Lee Harvey Oswald was linked to the Central Intelligence Agency (CIA).

A 1975 CIA memo says a thorough search of agency records in and outside the United States was conducted to determine whether the assassin had been used by the agency or connected with it in "any conceivable way."

It said the search came up empty, adding there was also no indication that any other US agency had used Oswald as a source or for recruitment.

It was released, along with another 676 government documents related to the November 1963 assassination, by The National Archives.

It is the third public release so far this year. Under law, all the documents were to be disclosed to the public last week.

Another CIA message sent two days after Kennedy was killed said an "important question" that remained unsolved was Oswald’s trip to Mexico City shortly before he fatally shot the President.

Officials were trying to determine the purpose of The CIA was trying to determine if Oswald had visited the Soviet embassy to obtain a visa so he could escape after the assassination.

While the Federal Bureau of Investigation said it interviewed Oswald upon his return, the CIA has consistently denied having done so.

The message said that although it appeared Oswald "was then thinking only about a peaceful change of residence to the Soviet Union, it is also possible that he was getting documented to make a quick escape after assassinating the president."

Oswald defected to the Soviet Union in 1959, petitioning for citizenship and later moving to the city of Minsk before returning to America in 1962.

Another record produced in April the following year recounted a visit to the CIA by three staff members of the Warren Commission, which was set up to investigate the assassination.

The memo said the staff members indicated that Thomas Mann, former ambassador to Mexico and then-assistant secretary for inter-American affairs, "still has the 'feeling in his guts' that (Cuban leader Fidel) Castro hired Oswald to kill Kennedy.

The assassination of JFK – in pictures Show all 8 1 /8 The assassination of JFK – in pictures The assassination of JFK – in pictures President John F. Kennedy and his wife Jacqueline Kennedy ride with secret agents in an open car motorcade shortly before the assassination, 22 November 1963 Getty The assassination of JFK – in pictures President John F. Kennedy and his wife Jacqueline Kennedy prior to his assassination Keystone/Getty The assassination of JFK – in pictures Kennedy is struck by an assassin's bullet as he travels through Dallas in a motorcade In the car next to him is his wife Jacqueline and in the front seat is Texas governor John Connally Three Lions/Hulton Archive/Getty The assassination of JFK – in pictures The view from the sixth floor window of the Texas School Book Depository in Dallas, from which Lee Harvey Oswald is thought to have assassinated Kennedy. This photograph was taken approximately one hour after the assassination Hulton Archive/Getty The assassination of JFK – in pictures Lee Harvey Oswald during a press conference after his arrest in Dallas. Lee Harvey Oswald was killed by Jack Ruby on 24 November on the eve of Kennedy's burial AFP/Getty The assassination of JFK – in pictures Lyndon B. Johnson takes the oath of office as President of the United States on the day of Kennedy's assassination. Jackie Kennedy is stood next to Johnson Getty The assassination of JFK – in pictures Kennedy's funeral procession goes into Arlington Cemetery in Washington Newsmakers/Getty The assassination of JFK – in pictures Kennedy's casket sat in the East Room of the White House Newsmakers/Getty

They said, however, that the commission has not been able to get any proof of that."

Also in the latest release was a 20-page FBI analysis of civil rights leader Martin Luther King Jr dated March 12, 1968 — a month before he was assassinated. One section alleges that King was attracted to former member of the Communist Party in America. It notes that two previous aides were party members and eight others, who helped shape King's organization in its early stages, had communist affiliations.

The analysis said that in the early 1960s, the Communist Party was trying to get a black labor coalition to further its goals in the United States. It referenced a May 1961 issue of a communist newspaper that stated, "Communists will do their utmost to strengthen and unite the Negro movement and ring it to the backing of the working people."