Fifty years after her tragic murder at the hands of Charles Manson’s cult followers, actress Sharon Tate is in the limelight again – her innocent and playful persona embodied by Margot Robbie in Quentin Tarantino’s “Once Upon a Time in Hollywood.”

But also five decades on, one California family is still grappling with the notion that one beloved member was possibly slain by followers of the satanic hippie “family,” yet it was swept under the rug.

His name was Filippo Tenerelli.

“It is absolutely frustrating, there is no doubt in my mind that Filippo was murdered. The evidence is undeniable and facts are facts,” Debra Tate, 66, the younger sister of the late Sharon, told Fox News. “This absolutely warrants another look.”

It was Tate who, in 2007, reached out to the Bishop Police Department in California’s Eastern Sierra and urged them to re-open the case, which they did at the beginning of 2008.

“It was a meager attempt for me to try to do the right thing and have them take a second look. Instead my plea was met with more cover-ups and sweeping it under the rug," Tate claimed. "This still warrants being looked into properly at the very least. This has amounted to extreme pain for Filippo’s family. I don’t know how these people can live with themselves.”

Author and investigator Tom O’Neill has shed uncomfortable light on the Tenerelli case in a chapter of his new book “Chaos: Charles Manson, the CIA and the Secret History of the Sixties” – a 550-page profound dive, 20 years in the making, into the plethora of inconsistencies and glaring holes punctuating the formal Manson narratives to date.

As the story goes, in late September of 1969, 23-year-old Italian immigrant Tenerelli left the family home in Culver City, Los Angeles in his '69 blue Volkswagen Beetle, bound for Death Valley National Park. The official theory at the time was that he intended to kill himself at an outlook, but his vehicle got wedged on boulders and in frustration he tipped it off the cliff. Then, he supposedly trudged down the rugged 400-feet terrain to retrieve his belongings, and somehow over the next couple of days wound up 100 miles away in Bishop, a city of 3,000 in California’s Inyo County, where he checked into the local Sportsman Lodge motel as “John Doe” before heading out to buy a shotgun.

The next morning, October 1, a maid tried to enter the room, which was barricaded from the inside. The son of motel owner Bea Greer pushed it in and found a body with a shotgun blast to the front of the head – having allegedly pulled the trigger with his toe. His pubic hair was shaved and a copy of “Playboy” between his legs.

The “suicide victim” was identified as the missing Culver City man a month later.

“But the case was soon pushed from the local papers by an even wilder story: in a remote area of Death Valley, a band of nomadic hippies had been arrested for destroying government property and operating an auto-theft ring,” O’Neill wrote. “In the coming weeks, they’d be charged with the grisly murders of Sharon Tate and seven others in Los Angeles.”

In addition to taking over the infamous Spahn Ranch outside of Los Angeles, Manson and his vicious band also spread themselves more than 200 miles east to the primitive Barker Ranch, inside Death Valley National Park.

A 1970 Rolling stone article detailing the grim Manson murder trail makes mention of Tenerelli’s suspicious “suicide,” and how some authorities were “not so sure” that was indeed the cause of death. But any internal investigations, O’Neill’s book shows, seemingly dissolved.

“The story got even murkier when I tracked down the original Bishop Police Department investigative report, which suggested a far more sinister ending and a cover-up of that,” O’Neill wrote, highlighting that his efforts since 2007 to pinpoint that ending have been dismissed and denied by an array of authorities.

He pointed out that, in spite of the bureaucratic account that the windows of the room would have been too small for a person to climb out of, he tracked down the relocated property at a nearby ranch and argued that even two people could fit through, which was backed up by the now 81-year-old motel owner.

Greer, according to O’Neill, also claimed that she would never have checked someone in without ID and gave registration records to police at the time – but the authorities’ “refused to believe that the victim had shown an ID or even a wallet.”

Although the customer always fills out their own form, Tenerelli’s name was allegedly spelled wrong – with his sister later affirming that it wasn’t his handwriting – O’Neill observed, with another red flag raised by the claim that the person who checked in under the name allegedly had no accent and paid a month in advance “to ensure that the body wouldn’t be discovered right away.”

O’Neill further points out that the police reports “contained no photographs of the crime scene and made no mention of forensics” even though they were commonplace in 1969, and the autopsy showed at the time of death, the body's blood alcohol was .03 percent – not even qualifying as under the influence – but a bottle of whiskey was found in the trash by his body and a second bottle only half full.

“If Tenerelli didn’t drink all that whiskey, who did?” O’Neill speculated.

A trove of further questions have also been unearthed – including allegations that a Culver City hospital radiologist had determined that the “John Doe's” x-rays were “similar or identical” to a patient – Tenerelli – who had been brought in after a motorcycle accident five years earlier, weeks before a formal police identification.

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Moreover, O’Neill asserts that the surgeon who conducted the autopsy told him that he never believed it was a suicide and called it that “under pressure” while California Highway Patrol officers who found the abandoned car on October 5 believed it could not have been there for more than two days – but the body was found on October 1.

Inside the vehicle, O’Neill writes, were other items indicating that the driver “might not have been alone in the car” such as a Brentwood Hospital laundry sheet, where Tenerelli had not been known to visit, and a Santa Monica bus schedule which “he wouldn’t have needed because he owned a car and a motorcycle.”

Deepening the deluge of questions, two hunters allegedly spotted someone “coming up from the wreck” of the car and there was a copious amount of blood – implying far more wounds than those believed to have been on the man when he showed up at the motel.

Meanwhile, the hippie car thieves had been taken into custody around October 1 – earlier, highway patrolmen were reported to have pulled over a “late model” blue Volkswagen a day prior to Tenerelli’s death, with three “hippie types” in the car, the patrolman later linking at least one member to a Manson follower. Both officers, O’Neill reported, also refuted the suicide avowal and instead surmised that the car was possibly dumped after the death.

Furthermore, there was the issue of the shaved pubic hair.

The Manson Family’s Bill Vance had a ‘magic vest’ he liked to wear that was ‘made of pubic hair,’ per a report from the Los Angeles County Sheriff’s Office, O’Neill underscored.

“I can only speculate as to what happened in Bishop (with the police) in 1969,” O’Neill told Fox News, indicating that perhaps they did not want their town linked to the Manson family or that some may have had teen relatives loosely connected to the family, or maybe it was simple incompetence or just that it was far easier to declare a suicide than a homicide.

Manson members were subsequently arrested in separate raids across California on October 10 and 12.

A spokesperson for the Bishop Police Department declined to comment on O’Neill’s book or whether any further action will be taken to investigate the Tenerelli case, other than to say that the information brought forward was “interesting” but that everyone initially involved was no longer there.

Cosimo Giovine, the southern California-based nephew of Tenerelli and the representative for the family, told Fox News that as deeply Catholic Italians, the suicide ruling had left a tremendous black scar on the family.

“Our family felt very ashamed, and couldn’t go back to Italy. My grandmother, even in her 90’s, always said she knew Filippo didn’t commit suicide,” he said. “But there is so much misinformation out there; we just want to know the truth.”

The Bishop Police Department confirmed to Fox News that the case, which was re-opened more than eleven years ago, has since been closed once again.

A letter viewed by Fox News from Inyo County District Attorney Thomas Hardy in May, 2016 to Giovine – who had submitted to his office a plethora of documents and testimonies gathered by O’Neill – stated that there was “simply not much” that they could do after 46 years and that “there is nothing in the material provided that suggests that there was any culpability on the part of the Department which would justify a criminal investigation” by the DA’s office.

Hardy did acknowledge that while “Mr. O’Neill’s work raises questions, it doesn’t point toward any answers that could hold up in court” and a new investigation could not be justified at that point.

Giovine then attempted in November 2016 to obtain copies from the Los Angeles Police Department of the tape recordings and transcripts of the conversation between Bill Boy and Charles “Tex” Watson along with “confirmation or denial that the name Filippo Tenerelli is mentioned in the tapes” – but to no avail, with the tapes in question still under seal. The tapes contain the first recorded account of how and why the murders took place, and unconfirmed claims have been made that Tenerelli’s name is raised by Watson. At 73, he remains behind bars in Texas.

Moreover, the nephew’s efforts in 2017 for a request for an investigation by the Inyo County Grand Jury were rejected, with Foreman John Harris writing “we feel that the 48-year-old events are beyond our ability to adequately investigate and report on at this time.”

But Tenerelli’s family isn’t ready to walk away. Giovine emphasized to Fox News that his intention is not to ask for money or to file lawsuits, but to have his uncle’s death certificate changed to reflect what he believes to be the true cause-of-death: homicide.

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And beyond advocating for the Tenerelli case, Debra – who has dedicated her life to serving as a spokesperson for the families of murder victims – is also still fighting relentlessly to ensure that the Manson murderers aren’t released.

She runs NoParoleforMansonFamily.com and individual petitions to ensure that the killers – two of who are now facing parole hearings in California – aren’t given the green light to walk the streets again.

“These people are much more prolific killers than anyone knows,” added Tate, whose emotions are still raw despite the passage of time. “There is no one else but me left in our family, the stress of what happened to my sister has killed everyone. But if she can’t live and be free again, then these killers should not be able to either.”