A madman who threatened to kill the rest of the Kennedy family after the assassination of Robert F. Kennedy in 1968 almost snuck onto the plane housing the assassinated politician's body, the FBI's newly released files, declassified Friday, reveal.

An initial report said the suspect, who Los Angeles police later identified as William Frederick Crosson, was just 100 yards from the airplane, although it later emerged he was arrested at a bar near the airport, according to the FBI report.

"He had been making death threats against the FBI, the Secret Service and the Kennedy family at the airport and at the bar in which he was arrested," said the June 6, 1968, FBI report, which noted he was taken in by the Los Angeles Police Department.

At the same time, police issued a bulletin for the arrest of a "female Caucasian" between the ages of 23 and 27 who was seen with Kennedy's assassin, Sirhan Sirhan, just before the shooting, which took place in the first minutes after midnight on June 5, inside the Ambassador Hotel.

The documents, released by Tulsi Gabbard, director of national intelligence, following a campaign promise from Donald Trump, show the panic of FBI field office across the country as agents processed myriad tips and reports of suspicious individuals in the hours after Kennedy was shot.

He died of his injuries in the early morning of June 6, two days after winning the California Democratic primary.

The Birmingham FBI office reported that an Alabama man named Frank Guthrie stated "they" should "have got Ted also," referring to RFK's brother Ted Kennedy, US Senator from Massachusetts.

In New York City, the FBI reported a man named Michael Cornelius "telephonically advised" how a man came up to him on the corner of 9th Avenue and 17 Street to let him know the train tracks near Washington's Union Station were mined and would explode when Kennedy's funeral train was scheduled to arrive on June 8 for his burial at Arlington National Cemetery.

A search of Sirhan's bedroom in Pasadena where he lived with his mother and three siblings revealed numerous menacing handwritten notes, including one written on May 18, 1968.

"My determination to remove RFK is becoming more the more of an unshakeable obsession. RFK must be disposed of like his brother was," one note included in the file reads.