When Hoover reconstituted COINTELPRO, Tom O’Neill explains (in Chaos: Charles Manson, the CIA, and the Secret History of the Sixties), he was already worried that America’s black militants would be embraced by liberal whites, especially in a left-leaning place like Hollywood:
In the August 1967 memo reanimating the counterintelligence program, he’d noted the importance of “prevent[ing] militant Black Nationalist groups and leaders from gaining respectability”: “they must be discredited to the white community, both the responsible community and to the ‘liberals’ who have vestiges of sympathy for militant black nationalists simply because they are Negroes.”
Two years later, the Panthers had become almost synonymous with Hollywood’s liberal elite. Actresses such as Jane Fonda and Jean Seberg appeared at their rallies. Hoover felt he had to widen the chasm between blacks and whites in Los Angeles. In a November 1968 memo, an L.A. field agent discussed new efforts to spread disinformation to Hollywood’s liberal whites.
In the context of the Tate–LaBianca murders, the memo is chilling. Remember, the Tate house by then had become a high-profile gathering place for liberal Hollywood—among others, for Fonda, Cass Elliot, and Warren Beatty, all three of whom were under FBI surveillance. Abigail Folger, who would die at the hands of the Family, was an outspoken civil rights activist. That year she campaigned for Tom Bradley, the first African American candidate for mayor of Los Angeles. Many in the Polanski–Tate crowd belonged to the White Panther party, explicit allies of the Black Panthers, or to the Peace and Freedom Party of California, which also voiced its support. The FBI, according to the memo, planned to generate distrust through disinformation:
The Peace and Freedom Party (PFP) has been furnishing the BPP with financial assistance. An anonymous letter is being prepared for Bureau approval to be sent to a leader of PFP in which it is set forth that the BPP has made statements in closed meetings that when the armed rebellion comes the whites in the PFP will be lined up against the wall with the rest of the whites.
[…]
Less than a year after this memo was written, Manson’s followers lined up four denizens of liberal Hollywood in Roman Polanski’s home and cut them to pieces, leaving slogans in blood to implicate the Black Panthers.