Debra Tatewas 16 years old when her sisterSharon Tatewas murdered. Since then, she has made it her life’s mission to keep her sister’s memory alive — and to keep the killers in prison.

On Aug. 9, 1969, police discovered the bodies of 8-months-pregnant actress Tate, Jay Sebring, Abigail Folger, Voytek Frykowski and Steven Parent at Tate’s house in Benedict Canyon. The next day, the slain bodies of Los Angeles grocer Leno LaBianca and his wife Rosemary were found in their Los Feliz home, about nine miles away.

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The murders have been covered in books, television shows and movies, includingQuentin Tarantino‘s 2019 filmOnce Upon a Time in … Hollywood, which stars actorsMargot Robbieas Sharon Tate andEmile Hirschas Jay Sebring. With every mention and new portrayal, the families of the victims are forced to grieve all over again.

Debra Tate.Jordan Strauss/Invision/AP/Shutterstock

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While Manson and cult members Susan Atkins, Patricia Krenwinkle, Leslie Van Houten and Tex Watson were initially convicted and sentenced to death for the murders, their sentences were reduced to life in prison when California abolished the death penalty for a time in 1972. Since then, Debra has attended each of the killers’ parole hearings to speak on behalf of the families who can’t attend, and often submits supporting signatures obtained through her website, NoParoleForMansonFamily.com.

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“The emotional pain is great because you have to go through the circumstances of the crime,” Tate, now 66, tells PEOPLE. “You relive it all. These people are still a danger to society. I spend my life trying to keep society safe.”

Anthony DiMaria.Gary Coronado/Los Angeles Times/Getty

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Sebring’s nephew Anthony DiMaria, who plans to release a documentary about his uncle’s life as a businessman and hairstylist, says his family attends the parole hearings on behalf of all of the victims.

“The murders were so profound, so severe, that the very least they can do is serve the rest of their lives behind bars,” he says. “Unless every one of the victims get out of their graves and live the 50 years they should have lived with us and all of their friends who loved them, there is no closure.”

source: people.com