To many, the bloodbath exposed the scary underside of the counterculture movement and seemed to mark the end of the peace-and-love era that burst upon the country just two years earlier during San Francisco's Summer of Love.
"The 'Summer of Love' was more a media event than anything else," Todd Gitlin, one of the nation's foremost historians of the 1960s, told The Associated Press in an email Wednesday. "But if hippie paradise was a myth, it was a myth that a lot of people believed in. Manson damaged it gravely."
On Wednesday, Manson, now a grizzled, shuffling 82-year-old, lay hospitalized with an undisclosed illness after being taken from California's Corcoran State Prison, where he was serving a life sentence, according to news reports that correction officials would not confirm, citing privacy laws.
His reappearance in the news conjured a turbulent period in U.S. history when the country seemed to be coming apart at the seams.
A petty criminal who had been in and out of jail since childhood, Manson reinvented himself during the Summer of Love as a long-haired, Christ-like guru spouting Bible verses and Beatles lyrics.
After attracting a few dozen followers from San Francisco's Haight-Ashbury district, many of them young women, runaways or other lost souls, he took them to an old movie ranch on the edge of Los Angeles that he transformed into a commune of sex, drugs and music.
On Aug. 9 and 10, 1969, he sent some of his devotees out on a murderous mission to two of Los Angeles' wealthiest neighborhoods, where they killed pregnant actress Sharon Tate, several of her society friends and others. Most of the victims, including coffee heiress Abigail Folger, were stabbed.
Tate's husband, Oscar-winning director Roman Polanski, was out of the country at the time.
Authorities would learn that Manson had hoped the killings would touch off a race war. He had apparently gotten the idea from a twisted reading of the hard-rocking Beatles song "Helter Skelter."
The slayings shocked the country with their savagery. Messages like "Pigs" and a misspelled "Healter Skelter" were scrawled in the victims' blood on their walls and doors, and the city was paralyzed in fear. Residents of Los Angeles' nearby Laurel Canyon neighborhood, then a haven for musicians, began locking their doors.
The youngest member of the original Manson Family, Leslie Van Houten, a teenage runaway and former homecoming princess from a Los Angeles suburb, said he had brainwashed her and others with sex, LSD, constant readings from the Bible, repeated playings of the Beatles' "White Album" and rambling lectures about triggering a revolution.
Like other surviving followers who took part in the killings, Van Houten is serving a life sentence for murder. A parole board recommended her release last year but was overruled by Gov. Jerry Brown.
Another Manson Family member, Lynette "Squeaky" Fromme, was never charged in the so-called Tate-La Bianca murders but went to prison later for trying to assassinate President Gerald Ford in 1975. Fromme, whose gun didn't fire, was paroled in 2009 after 34 years behind bars.
After Manson and his followers were caught, the nation got a front-page look at his piercing, demonic stare and the Nazi swastika he carved into his forehead during his trial.
The killings - along with a deadly stabbing in December 1969 at a free concert headlined by the Rolling Stones at the Altamont Speedway outside San Francisco - contributed to the sense that the era of peace and love that seemed to reach a high point at Woodstock in the summer of 1969 was over, the dream turned into a nightmare.
But in her book "The White Album," writer Joan Didion indicated people living in Los Angeles at that time shouldn't have been that surprised.
"This mystical flirtation with the idea of 'sin' - this sense that it was possible to go 'too far,' and that many people were doing it - was very much with us in Los Angeles in 1968 and 1969," she wrote. "A demented and seductive vortical tension was building in the community. The jitters were setting in."
During a 2013 Rolling Stone interview, Manson had seemingly lost none of his attitude - "If I can touch you, I can kill you," he told reporter Erik Hedegaard - but did not appear to be aging well.
"He's an old man with a nice head of gray hair but bad hearing, bad lungs, and chipped-and-fractured, prison-dispensed bad dentures," Hedegaard wrote, adding that Manson shuffled when he walked and used a cane.