Perhaps [Sharon Tate's and Roman Polanski's] best friends during this [late 60s] period were Mia Farrow and Peter Sellars. Since her separation from Frank Sinatra, Mia had grown closer to Sharon, and often spent weekends with her and Roman. It was Roman who first introduced Mia to Sellars, whom he had met during the filming of Rosemary's Baby. Polanski had taken an instant liking to the rather quiet and thoughtful man who, in private, was so different from his jovial public personality. Roman later remembered both Mia and Peter as being intoxicated with the late 1960s counterculture and all that went with it -- Indian clothing, beaded chains and necklaces, meditation and astrology.

-- from Sharon Tate and the Manson Murders by Greg King

Per Cynthia, in "John", she and John met Sharon and Roman at a party in London...

There was that weird episode, during one of John's drug-fueled rampages in Los Angeles, in which Lennon raged against Roman Polanski in a way that nobody could make sense of.

Polanski *was* a creep, but while Sharon Tate figured this out early on, I don't think it was generally known until after he was arrested for having inappropriate sexual relations with a young girl.

Do you mean the night he yelled "It's all Roman Polanski's fault?"

Yeah! And he was smashing Harold Seider's apartment to pieces.

I think there was a reason for John's complaining about Roman Polanski, but it has to do with John's original destiny...