In 1971, cult leader Charles Manson was sentenced to death for murdering two people and orchestrating the killings of seven others in August of 1969. But why, if he received the death penalty all those years ago, did he spend his life in jail, dying of natural causes in 2017?

It all has to do with a couple of court cases that suspended the death penalty the year after Manson was sentenced. These cases effectively struck down all methods of state execution in the U.S. for four years, leaving Manson and his followers with the next harshest sentence at the time in California—life with parole.

“At the time that Manson and his followers were sentenced to death, California did not have a life without parole sentence,” says Hadar Aviram, a law professor in California who is writing a book about the Manson Family parole hearings, titled Yesterday’s Monsters. So when the death penalty was taken away, Manson and his followers were bumped down to a sentence in which they would not only live, they would have a chance to walk free.

This series of events was kicked off in February of 1972 with the case of People v. Anderson, in which the California state Supreme Court struck down the death penalty, arguing that it constituted cruel and unusual punishment. Later that year, Californians voted to reinstate the death penalty with Proposition 17, but it didn’t have any effect—that summer, the U.S. Supreme Court had effectively halted all executions in the country.

This federal decision came from a case known as Furman v. Georgia, in which the court found that the Georgia’s death penalty system disproportionately executed people of color, gave juries no parameters for how to settle on a death sentence, and was riddled with other procedural issues.

“The Supreme Court therefore decided that the death penalty in that incarnation, given those procedural problems, violated the due process clause of the Constitution,” Aviram says. No other state at the time met the Supreme Court’s requirements, “so that meant that now states had to figure out how to get around these procedural problems and create a death penalty that would comply.”

Georgia became the first state to start executions again in 1976, but for four years there was no viable way to sentence someone to death in the United States. California didn’t begin an approved execution system until 1978, the same year that it developed a sentence of life without parole. Both of these developments in California were heavily tied to the fear that Manson and his cult members would one day walk free.

The public had been horrified by the murder of the pregnant actress Sharon Tate and four others at her Beverly Hills home on August 9, 1969. Manson hadn’t even known Tate lived there; he’d intended his followers to find the house’s former resident, a music producer who’d failed to get Manson a recording deal. The next day, his followers murdered a married couple, the LaBiancas, in their home. Manson believed that these murders would trigger an inevitable race war that he called “Helter Skelter,” after The Beatles’ song.

The murder scenes were particularly gruesome. The cult left their victims with multiple stab wounds, and Susan Atkins, one of the murderers, had written “pig” on the front door with Tate’s blood. These terrifying details captivated the public, making the very real possibility that Manson and his cult could get parole even more alarming.

“In the ‘70s, it was quite normal for someone convicted of murder to get out after 10, 15 years,” Aviram says. Like everyone serving a life sentence in California, the Manson cult members came up for parole after the first seven years of their sentences, “and there was real concern in the public that at least the women, if not everybody else, were going to get out fairly quickly.”

Even though the introduction of these harsher sentences was meant to protect against future murderers getting out on parole, these new charges couldn’t be applied to Manson or his followers. Aviram says that although sentences can be retroactively reduced—like when Manson’s death sentence was commuted in 1972—they cannot be increased. Therefore, when California adopted a life sentence without parole and a new death sentence in 1978, Manson attended his first parole hearing; and he continued these parole hearings until the very end.

Aviram says the possibility of Manson gaining parole was never very likely because he didn’t take the hearings seriously (at the first one, he sang). During the 1980s, he developed serious health problems after an inmate set him on fire, which he could have used to pursue parole on medical grounds. But according to Aviram, he never did.

Deborah Tate, sister of the late Sharon Tate, has shown up to cult members’ parole hearings to protest their release since the very beginning. So far, none have been granted parole, but two have been recommended for it, and could conceivably be released in the future: 75-year-old Bruce Davis and 68-year-old Leslie Van Houten.

California Governor Jerry Brown already rejected Davis’s parole recommendation in June 2017, and has rejected a previous recommendation for Van Houten. But as of Manson’s death, Brown had yet to approve or reject Van Houten’s most recent recommendation for release.