Washington (CNN) -- He buried two older brothers killed by assassins' bullets, and FBI files released Monday showed that Sen. Edward Kennedy was the subject of seemingly endless threats throughout his political career.
The more than 2,000 pages made public included threats that ranged from the obscene ramblings of troubled people to angry warnings of death and violence against Kennedy, who was a U.S. senator from Massachusetts from 1963 until his death in 2009. Many of the documents, including poor-quality mimeographs of news articles and official government memos, have handwritten notations on them, presumably by FBI officials who looked them over.
A particular focus of the threats, profane messages, defaced photos and other items was the 1969 auto accident in which a car driven by Kennedy ran off a bridge on Chappaquiddick Island -- part of Martha's Vineyard -- resulting in the drowning death of the lone passenger, Mary Jo Kopechne.
"Ted target #3 killer of Mary Jo," read one handwritten note on an election campaign news article in 1970. Another handwritten note referred to the 1963 assassination of Kennedy's brother President John F. Kennedy, saying: "Body guards don't mean thing jack had them but the bullet got him."
In response, the FBI monitored the constant tips, warnings, conspiracy theories and allegations of a coverup they received, with former Director J. Edgar Hoover sometimes personally involved, the files show.
In a letter to a woman in Collingswood, New Jersey, on July 28, 1969, Hoover thanked her for writing him with her "concerns" about the Chappaquiddick accident and then added: "There is no indication that the death of Miss Mary Jo Kopechne involved the violation of any federal law within the jurisdiction of the FBI."
In a June 12, 1968, entry, shortly after the assassination of Robert Kennedy, Hoover called for Edward Kennedy to get "all the protection he needs," adding: "We are down to one Kennedy."
In another section, a 1964 memo from Hoover to Kennedy revealed that Kennedy's father, influential financier and diplomat Joseph Kennedy, once offered Hoover significant backing for a possible presidential election bid in 1955.
Hoover wrote that he told the elder Kennedy he had no political ambitions and could best serve the country in his position with the FBI.
The files released Monday were in response to Freedom of Information Act requests by several media organizations, including CNN.
There was no comment Monday from Kennedy's family.
The FBI files covered 1961 to 1986, from just before Kennedy's election to fill the Senate seat vacated when John F. Kennedy became president to several years after his own presidential aspirations ended, when he lost the 1980 Democratic nomination to President Jimmy Carter.
While Kennedy was no longer a serious candidate for president, the threats continued. An entry dated May 23, 1985, detailed a profanity-laced threat against Kennedy and then-President Ronald Reagan.
"Brass tacks, I'm gonna kill Kennedy and Reagan and I really, really mean it," read the threat, according to the FBI file. A footnote at the bottom of the file page said: "Due to nature of the threats, consider subject armed and dangerous."
In a later entry, a psycholinguistics report concluded that "the author is merely ventilating her frustrations and projecting her inadequacies. Her intention is to shock in order to gain attention."
"Although the subject's ideation is clearly paranoid, the message lacks the indicators of the resolve or the determination to carry out her threats," said the report. Charges in the case were dropped in 1986, according to the file.
Threats also extended to other members of the Kennedy family, one of the nation's most influential political dynasties. In a 1974 letter to then FBI Director Clarence Kelley, Kennedy expressed gratitude for "the unusual attention and service performed by the members of your Bureau in the recent possible threat against our children."
"The Bureau's advice and guidance was of great comfort to all of us, particularly to my sister-in-law Ethel," Kennedy wrote in reference to Ethel Kennedy, the widow of his brother Robert.
In 1976, Kelley wrote Kennedy a glowing note after arranging for the senator and his two sons to tour the FBI.
"I don't know that I have seen two better behaved young men than your two sons," Kelley wrote, congratulating Kennedy for "obviously showering them with love and attention."
"They reflected that very visibly in their treatment given you," Kelley wrote. "They most definitely adore you. No father could ask for more."
More reflective of the files was a 1975 letter received by former Vice President and Sen. Hubert H. Humphrey that noted Humphrey was boosting Kennedy as a possible presidential nominee.
"Don't you know that there are millions of us that don't like the (expletive) Kennedys, noteably the women, they still remember how he swam off to save his dirty hide and left Mary Jo to drown in his car," the letter said. "That showed what kind of S.O.B. he is. He should live in the cemetery with John and Robert. So let him run for President if he dares and some one will knock him off just like they did his brothers."
CNN's William Mears, Pam Benson, Jim Barnett, Terry Frieden, David DeSola, Jeanne Meserve, Rachel Streitfeld, Carol Cratty and Tom Cohen contributed to this report.