Hollywood actress Sharon Tate -- then eight months pregnant -- was stabbed to death Aug. 9, 1969, along with four others in the home she shared with director Roman Polanski.
The next day another well-known couple was brutally murdered. Wealthy businessman Leno LaBianca and his wife, Rosemary, were killed in their Los Angeles home.
The murders were at the hands of a small group led by Charles Manson. The murders, he had told them, would ignite an apocalyptic race war. Many said at the time the grisly crimes brought an end to the decade of love.
Vincent Bugliosi, the former Los Angeles prosecutor who convicted Manson in 1970, says that these murders could not have happened without Manson.
"He would have killed as many people as he could have. That was his religion," Bugliosi said. "These people killed with relish."
More twisted than Manson's vision was his ability to turn four people, three of them young women from middle-class families, into eager killers who laughed when they were on trial.
Manson and his so-called "family" were sentenced to death. But when the state of California abolished the death penalty in 1972 their sentences were commuted to seven years to life. At the time there was no life without parole.
Now with the 40th anniversary of the murders there are fresh calls for the release of two of Manson's followers.
It was Susan Atkins who stabbed Sharon Tate to death while the pregnant actress begged her to stop. It was a moment described at Atkins' parole hearing years ago.
"She asked me to spare her," Atkins said. "I told her I didn't have any mercy for her."
Atkins, now dying of cancer, is asking she be released from prison after 39 years so she can die in hospice.
Her next hearing is scheduled for September 2. Atkins husband will argue releasing his wife to die at home would save the state $10,000 a day in hospital charges.
"She can nod her head and look left and right. ... She has limited use of her left arm," Waterhouse said. "She's expressed remorse and grief for every one of her parole hearings going back to 1972."
Meanwhile, Leslie Van Houten is now pleading for parole, too -- something she has been denied 18 times.
The former homecoming queen once said she wished she had been there the night Susan Tate was murdered.
But the next night she was involved with stabbing Rosemary LaBianca 16 times.
In 1994, while in prison, she sat down with Diane Sawyer who asked her how she lives knowing what was inside her.
"It's not easy," Van Houten said. "If anything, the older I get the harder it is. I took away all that life."
Filmmaker and author John Waters began a close friendship with Van Houten after she turned him down for an interview for a piece he was writing for Rolling Stone magazine. He visited her dozens of times over the years and is now publicly arguing for Van Houten's parole.
"She has apologized many, many times," Waters said. "She is the poster girl for the California prisons, I think. She went in a complete lunatic and came out, if she ever does, an incredibly mature woman."
But a retired prosecutor, whose job it was to argue against the murderers' release at 60 parole hearings, makes the same argument today.
"If they're doing good things in prison I applaud them," said former Manson prosecutor Stephen Kay. "But do they deserve to be outside in normal society? Not for what they did, no. Never."
Angela Smaldino, niece of the LaBiancas, was a college student in Los Angeles at the time her aunt and uncle were killed.
"I think they murdered people and they shouldn't ever get out of jail," she said. But Smaldino forgives "as a Christian."
She is also sympathetic about what Van Houten has lost in prison. What she'd like now is for her family's killers to reach out directly to her.
"Write me, Leslie ... let's talk about it," Smaldino said. "I'm going to make it a priority to heal. I don't want to carry this any further."
As for Waters who wrote about Leslie Van Houten in his upcoming book, "Role Models," he acknowledge there are no easy decisions in this case.
"I wanted at least to have a chance to stick up for my friend," Waters said. "I understand it's not a popular decision, but I hope people will consider it."
ABC News' Felicia Biberica contributed to this report.