As a member of Charles Manson’s infamous “Family”, Leslie Van Houten took part in perhaps the most notorious killing spree in California history. In the summer of 1969, as Manson sought to spark the race war he believed was imminent, the 19-year-old Van Houten became the youngest of his followers to participate in the Tate-LaBianca murders, which shocked the world and brought the counterculture of the 1960s to a bloody conclusion.

One of the original prosecutors at the subsequent, sensational trial said that Van Houten was the most likely of those convicted of the crimes to one day be eligible for parole. On Wednesday morning, 44 years after she was first imprisoned, she again took to the stand, hoping the time had finally come for her release. Now 63, her hair grey and her face lined by decades of incarceration, Van Houten faced a parole hearing – her 20th – at the California Institution for Women in Chino.

Explaining her involvement in the brutal killings, she said, "I twisted myself to the point where I thought this had to be done, and I participated… I did something that is unforgiveable, but I can create a world where I make amends… I'm trying to be someone who lives a life for healing rather than destruction."

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The parole board disagreed, and on Wednesday evening Van Houten was once again denied freedom. The board decided she could not seek parole again for another five years. Despite her defence team’s contention that she was simply an impressionable teen manipulated by Manson, prosecutors claim she was a willing and active participant in the murders of wealthy grocery owners Leno and Rosemary LaBianca in August 1969. They have the support of the victims’ families, who continue to oppose the release of any of Manson’s followers.

Van Houten’s lawyer Michael Satris said before the hearing that his client was a completely different woman to the one who took part in the slayings. "She is living a life of amends for her crime on a daily basis," Satris told the Associated Press. "Everything she does now is to be of service and benefit to the world." Though she is seeking release, he said, that was not the motive for her good works. "She just wants to be as good of a person as she can be. And it would be a matter of grace if the parole board would bestow on her the chance to accomplish this on the outside."

She has earned two college degrees during her time behind bars, and been praised for her work in supporting the elderly women inmates at her prison. Following her last parole hearing in 2010, Van Houten’s father Paul told reporters, “Leslie, my God, is unbelievable… I’ll guarantee you there are people on the outside who haven’t done as well.”

Born in Monrovia, California in August 1949, Van Houten was twice named her high school’s homecoming princess. But after her parents divorced when she was a teenager, she is said to have distanced herself from her family, and began regularly using marijuana and LSD. She was introduced to Manson in 1968 by a boyfriend, Manson Family member Bobby Beausoleil – who was himself later convicted of the murder of music teacher Gary Hinman.

Spellbound by the charismatic cult leader, she soon moved to Spahn Ranch, the old Western movie set outside Los Angeles that Manson and his followers had made their home. Van Houten said she came to regard Manson as Jesus Christ, and was swept up in his plan to murder at random and blame the slayings on African-Americans.

On 9 August 1969, members of the Manson Family killed the pregnant actress Sharon Tate and four other people at the LA home that Tate shared with her husband, the controversial film director Roman Polanski. Van Houten was not involved in the Tate killings, but the following night she went with Manson and several of his followers to the home of Leno and Rosemary LaBianca, who had also been randomly targeted for murder.

Van Houten struggled with 38-year-old Rosemary LaBianca, and then held her down as she was stabbed repeatedly. A Manson accomplice, Charles “Tex” Watson, handed Van Houten a knife and told her to “do something”, as Manson had made clear that he wanted everyone involved to incriminate themselves in the murders. Van Houten stabbed Mrs LaBianca around two dozen times in the back. She has since claimed that she believed her victim was already dead when she stabbed her. After killing the couple, the Manson Family members used their blood to scrawl hate messages on the walls of the home.

"Mr and Mrs La Bianca died the worst possible deaths a human being can," Van Houten told her latest parole hearing. "It affected their families. It affected the community of Los Angeles, which lived in fear. And it destroyed the peace movement going on at the time, and tainted everything from 1969 on."

Van Houten was the youngest of the defendants at the original trial, and widely considered the most likely to receive a recommendation for mercy, but she lost the sympathy of the jury by giggling during testimony about the murders. She was convicted and sentenced to death in March 1971, alongside Manson and two others, Susan Atkins and Patricia Krenwinkel. Their sentences were reduced to life in prison when the death penalty was outlawed in California between 1972 and 1977.

In 1977 Van Houten was awarded a retrial, which ended in a hung jury. During a subsequent third trial, she was set free on bail for several months, but found guilty again and returned to prison to serve out her life sentence. Atkins died of cancer in prison. Beausoleil, Watson and Krenwinkel have also been repeatedly denied parole. Another Manson follower and convicted murderer, Bruce Davis, was approved for parole last year, but the decision was reversed by California governor Jerry Brown.

Only one member of the Manson Family has been convicted of murder and later released: Steve “Clem” Grogan, who helped Manson to kill Hollywood stuntman Donald “Shorty” Shea. Grogan was sentenced to life in prison, but freed in 1985. Manson himself, who is now 78, has stopped attending parole hearings, saying that prison is now his home and he wants to stay there.