FBI files show threats against Ted Kennedy

(CBS/AP) BOSTON - Newly released FBI documents reveal threats against the late Sen. Edward Kennedy continued long after the assassination of his brothers.

Four years after Sen. Robert Kennedy was slain in Los Angeles in 1968, police received two letters warning Edward Kennedy against visiting Florida.

Police added more officers to guard Kennedy, and the soon-to-be owner of the New York Yankees George Steinbrenner hired up to 10 private security detectives to protect the Massachusetts Democrat.

The more than 1,400 documents made public Monday by the FBI also included the investigation of an envelope filled with white powder delivered to Kennedy's office during the anthrax scare following the Sept. 11, 2001 terror attacks. The white power tested negative for anthrax.

Kennedy died of brain cancer in 2009. More than 2,300 pages of his FBI file were released last year.