The killings of August 1969 reach most readers through one book. Helter Skelter, written by the prosecutor Vincent Bugliosi with Curt Gentry and published in 1974, became one of the best selling true crime works ever issued, and the motive it advanced at trial has served ever since as the accepted explanation: that Charles Manson expected an apocalyptic race war, believed the Beatles had encoded its approach in the White Album, and ordered the murders to begin it.
That account had a specific job to do. Manson was not present at the Cielo Drive killings, and the prosecution had to establish that he had directed them. A motive held by him alone, and followed by the others, supplied the link. Whether it was also the true explanation is a separate question, and several later writers have argued it was not, proposing instead that the killings grew out of drug debts and an attempt to exculpate an associate already in custody. Those accounts carry evidential problems of their own and none has displaced Bugliosi's, but the reason the argument persists is structural: the dominant narrative was produced by the party that needed it in order to convict.
Two things are not in dispute. The group formed around a man who had spent more than half his life in institutions and who drew a following from young people already adrift, using a vocabulary borrowed loosely from Scientology, the Process Church and popular apocalyptic. And the case did more than any other to fix the figure of the destructive charismatic leader in public imagination, several years before the vocabulary now used for such groups became ordinary.