Sarah Turney remains convinced that her father, Michael Turney, killed her sister Alissa Turney in 2001.

The host of the podcast Voices for Justice isn't the only one who thinks so, either, with several of Alissa's friends sharing that conclusion in Oxygen's new documentary Family Secrets: The Disappearance of Alissa Turney, premiering Oct. 13.

Michael, however, has repeatedly denied killing Alissa and was acquitted of murder in July 2023.

"I have no idea where Alissa is," he told NBC's Dateline last December, "alive or dead." He reiterated that he didn't know what happened to her in an on-camera 2024 sit-down with Sarah shown in Family Secrets.

In fact, no trace of Alissa has ever been found.

But Det. William Andersen of the Phoenix Police Department's Missing Person Unit, who caught the cold case in 2008, doesn't believe Alissa ran away, as her father reported to police on May 17, 2001.

"Cutting all ties with everybody she's ever known, that just doesn’t happen," the detective observed in the Oxygen doc. "That speaks to some deep psychopathy, or that suggests something nefarious happened to her. My job is to figure out what could have gone wrong."

But Sarah, who firmly believed in her father's innocence when Andersen first interviewed her in 2008 ("I was in complete denial," she said in the Oxygen doc), doesn't buy it.

Once she became convinced that he was capable of harming Alissa, she devoted herself to telling her sister's story. 

"It's really a story about how victims can find a new way to take control of the narrative," Jesse Sweet, who directed Family Secrets with Ricki Stern, told Oxygen.com, "to be active in the investigation, not be passive."

Who are Sarah Turney and Alissa Turney?

Michael, a former deputy sheriff turned electrician, was a father of three boys—Rhett, James and Michael Jr.—when he married mortage loan officer Barbara Strahm. She was mom to Alissa and her older brother Jon from a previous marriage. Michael and Barbara then had Sarah together.

"Step or half was not a word we were allowed to use," Sarah said in Family Secrets, noting that the Turney kids were told to think of each other as brothers and sisters, period.

Sarah was about 3 and Alissa 8 when Barbara was diagnosed with terminal lung cancer in 1992. She died the following year, after which Michael adopted Alissa. (Among the home movies shot by Michael that are sampled in the doc, one dated March 3, 1993, shows Barbara in an open casket during a viewing.)

Their older brothers had all moved away, Sarah said, and with her dad seemingly adrift, Alissa ended up doing most of the housework. She also started "experimenting with drinking," Sarah said. Sometimes she'd "tattle" on her older sibling, Sarah added, and they'd fight.

But, Sarah said, she never wanted Alissa to leave.

What happened to Alissa Turney?

Alissa went missing on May 17, 2001, the last day of her junior year at Paradise Valley High School. Sarah had just finished seventh grade.

Michael told police that he had picked the 17-year-old up early from school and taken her to lunch, according to authorities. Alissa demanded more freedom and they argued, he said, after which he dropped her off at home and went to pick up Sarah from a field trip.

In the doc, Sarah recalled her dad telling her that Alissa wasn't picking up her phone. When they got home, she continued, Alissa's cell phone and backpack were in her room, along with a handwritten note. 

The note, shown in the doc, relayed that Alissa had taken $300 from her stepdad and was headed to California. When Michael called police that night to report that his daughter had seemingly run away, Sarah said in Family Secrets, officers did not immediately come to the house to investigate.

Det. Anderson explained in the doc that runaway cases, especially ones in which there was a note and seemingly a sign of life in the form of that alleged phone call, often did not get the same attention as other missing-person cases.

"At the time, there were no signs of foul play or exigency based on the fact Alissa was 17 years old and had no mental/physical health issues,” Phoenix Police Sgt. Maggie Cox told NBC's Dateline in 2020. "Alissa was entered into NCIC [National Crime Information Center] as soon as the report was taken. In 2008, the Missing Persons Unit Detectives began to investigate further information obtained in the case."

But, Sarah said in Family Secrets, she believed at the time that Alissa really had run away, as did other family members.

Michael's second-eldest son, James Turney, told Dateline in 2020 that he last spoke to Alissa, who's 10 years his junior, a few months before she disappeared.

“She told me she was afraid of our father and wanted to leave," James said. "I told her she could come stay with me. And then when I found out she was missing, we 100 percent believed she had run away."

Still, Alissa had "so many options of places to go," James added. "But she just vanished."

A week after her sister disappeared, Sarah said in the Oxygen doc, her dad came into her room at 5 a.m. saying that Alissa was on the phone, cursing and telling him to leave her alone, after which the call cut out. Michael called the phone company, Sarah said, and the call was traced to a convenience store in Riverside, Calif.

They actually traveled to California and went to the store, Sarah continued, but there was no security footage and no way to trace who made the call. After that, Sarah said, she made her first missing poster and her dad put them up all over town.

When did Alissa Turney's case turn into more than a search for a runaway?

When Andersen got the case in 2008, multiple things bothered him about the theory that Alissa just up and left.

For one thing, Alissa left her phone behind, Andersen said, which was unheard of in his experience when it came to kids running away.

And as he detailed in the Oxygen doc, Alissa never tried to contact any family members, friends or her boyfriend Jon Laackman—whom Michael alleged was physically violent, Andersen said, but Jon denied it and the detective believed the teen.

More disturbingly, Jon also said in a videotaped interview with the detective that Alissa had told him that her stepdad had driven her to an "unoccupied area, the desert somewhere" and tried to "fool around" with her. "She had to get aggressive," Jon said, to fight him off. 

Two of Alissa's friends and one of her stepbrothers later told police that Alissa had shared a similar story with them, according to Andersen.

Michael has repeatedly denied accusations that he molested Alissa at any time. "I never did," he told Dateline in 2023, "and I would never do anything like that."

Andersen also learned that Michael had cameras set up all around the house, inside and out, and had been recording Alissa's phone calls. In addition to home movies, Family Secrets features audio and video clips from the surveillance Michael was conducting within his own home. 

Michael countered to police that Alissa was troubled and he had to keep a close eye on her.

"We thought it was crazy how overbearing he was," Alissa's friend Jessica Lang said of Michael in Family Secrets. Another pal, Charity Behrend, described Alissa as "very outgoing, very funny" and "curious about the world around her." Charity also said they mainly hung out at her house because Alissa didn't like being at home—until, she added, Michael forbid Alissa from seeing Charity, calling her a "bad influence."

Another home movie included in the doc shows Alissa, dressed up and headed out to prom with her friends, being told by her dad (who's behind the camera) that she can't go. She looks at him with disbelief as he insists he's serious. Ultimately the doc relays that she was allowed to go, but he demanded that she not leave the building once she got there.

In 2008, Michael refused to come in for a formal interview, Andersen said in the doc, but was "relatively cooperative" over the phone. But when he asked Michael to provide the tape from the day Alissa disappeared, the detective added, he "hems and haws."

Why was Michael Turney arrested?

The abuse allegations "finally forced [police] to look at my sister's case," Sarah told Dateline in 2020. "If you asked me then if I thought my father had any involvement, I would have said no. But over the years, he had so many renditions of what happened that day. Something wasn't right."

Sgt. Cox told Dateline, "The totality of circumstances known to police prompted the focus on Michael Turney as the suspect." 

And on Dec. 11, 2008, Phoenix police searched the Turney home in connection with Alissa's disappearance.

Investigators were mainly looking for documents, cassettes and videotapes, but to their surprise they found numerous guns, ammunition and 26 homemade pipe bombs, according to the FBI's Phoenix division.

They also found a van on the property that was full of containers of propane and bleach and had nails packed into the wheel wells, Andersen said in Family Secrets. As he detailed in the documentary, they also found several envelopes in a safe, each made out to a different news outlet and containing a thumb drive. On the drive was a manifesto, shown in the doc, in which Michael accused the electricians' union of being involved in Alissa's kidnapping and murder, and shared his plan to exact revenge by driving his homemade bomb of a van into the International Brotherhood of Electrical Workers' union hall.

The document was titled "Diary of a Madman Martyr."

When Michael was arrested that same day, he "had two pistols on his person," Det. Stuart Somershoe told ABC News in 2009. "He had seven magazines filled with ammo. He had a knife. He had a recording device."

On March 30, 2010, Michael pleaded guilty in federal court to one count of unlawful possession of unregistered destructive devices, a felony offense, according to the U.S. Attorney's Office for the District of Arizona.

"As a result of this prosecution, a dangerous man is off the streets," U.S. Attorney Dennis K. Burke said in a statement. "His self-built supply of bombs had the potential for catastrophic consequences."

Michael was sentenced to 10 years in federal prison.

Meanwhile, Andersen said in Family Secrets, authorities never found any surveillance footage from the day Alissa went missing, or any recording of the call her dad said she made a week later.

How did Sarah Turney end up suspecting her dad Michael Turney of killing her sister Alissa Turney?

Sarah said in Family Secrets that, when her dad went to prison, she fully believed that he was innocent and had been framed by authorities. She started a "Free Michael Turney" website and advocated for his release. 

Nor was she fazed by suspicion that he'd harmed Alissa. 

"We know he had nothing to do with the disappearance of my sister," Sarah told ABC 15 after he was locked up. "He's the best dad I could ask for." 

But as the years went by, she came to the opposite conclusion.

She read about the allegations of sexual abuse included in her sister's case file, and then went back and watched her dad's home movies, she explained in the documentary. In a 1997 video from a family camping trip sampled in the film, Alissa is heard shouting, "Dad's a pervert!" At the time, Sarah said, she thought nothing of it.

"While I thought my dad was basically a superhero and the best dad ever," Sarah said in Family Secrets, "it seems that he was a monster."

She continued, "My theory is, on the day she went missing, he picked her up and took her to the desert, tried it [sexually assaulting her] again, perhaps she fought back, something went wrong and he decided to kill her."

By the time Michael was released early from prison in 2017, Sarah fully believed in his guilt and had told police she'd do anything to help put him away. She recorded a conversation she had with her dad at a coffee shop, in which he denied killing or molesting Alissa. But she interpreted a comment he made—challenging Sarah to come to his death bed and see what he had to say then—as a confession. 

But, as Andersen said in Family Secrets, there was no physical evidence and no crime scene, and police couldn't use "snippets of a conversation" to make their case.

What Michael said, he added, was "not a confession to a homicide."

Determined to tell her sister's story, Sarah started a blog and appeared on various true crime podcasts. In July 2019 she launched her own podcast, Voices for Justice, interviewing Alissa's friends, delving into the case file, recounting her dad's explosives case and sharing her suspicions about Michael's role in Alissa's disappearance.

“I'm never going to give up," Sarah told Dateline in June 2020. "Alissa is my whole life. Finding out what happened to her has become my life."

Moreover, Sarah added, "She deserves her day in court. And I’m determined to give her that."

She also discovered plenty of true crime enthusiasts on TikTok and that's where, on Aug. 20, 2020, she shared with her followers that Michael had been arrested for Alissa's murder.

What happened at Michael Turney's murder trial?

Michael, charged with second-degree murder, pleaded not guilty. The 75-year-old looked frail and sat in a wheelchair when his case went to trial in July 2023.

The "whole case is based on circumstantial evidence, speculation, belief," defense attorney Jamie A. Jackson said in court, per video from the trial. "There's no evidence."

The defense also successfully moved to keep allegations of sexual abuse out of the proceedings, meaning the people who told police that Alissa had alleged her father tried to assault her could not say as much on the witness stand.

After the prosecution rested its case on July 17, 2023, following five days of testimony, the defense moved for a bench acquittal. Attorney Olivia Hicks argued that the state had not made "reasonable inference" that Michael killed Alissa.

Judge Sam J. Myers agreed and ordered Michael's release from custody.

"He is happy that the judge saw it his way," Jackson told reporters afterward, per NBC News. "He's excited that he'll be able to get out of custody. He is obviously still very concerned about the case and Alissa and trying to find who actually killed her."

Michael was released July 18, 2023. Jeopardy was attached, meaning he cannot be tried on the same charge.

Where is Sarah Turney now?

Disappointed but undeterred, Sarah continued to press her dad for answers. She sat down with him for a February 2024 conversation captured on camera for the Oxygen documentary in which he again denied molesting or killing Alissa and accused Sarah of destroying their family.

"I don't need a judge or a jury to tell me what we all know," she said in the doc after their heated exchange. "I'm at peace with what I've done for Alissa."

Since early 2021 she's been delving into other missing person and homicide cases on her podcast, explaining that part of her mission now is to help other families in their frequently frustrating quests for closure. 

But she hasn't abandoned her original motivation: Sarah said on the Oct. 3 episode of Voices for Justice that a new season about Alissa's case is "currently in development."

Family Secrets: The Disappearance of Alissa Turney premieres Sunday, Oct. 13, at 8 p.m. on Oxygen. An extended version premieres Tuesday, Oct. 15, on Peacock.

(E!, Oxygen and NBC are all members of the NBCUniversal family.)