Alissa Turney's Sister Recalls Dad's 'Odd and Off-Putting' Behavior Behavior Before Teen's 2001 Disappearance: Docuseries

For Sarah Turney, home videos of her childhood were something that would bring her “happy memories” for years.

But now? “Everything I see, I see in a different light,” she says in a clip from Oxygen's Family Secrets: The Disappearance of Alissa Turney, a new true crime docuseries, now streaming on Peacock.

Alissa vanished from their Phoenix, Ariz., home on the final day of her junior year of high school — a disheveled bedroom and a note left behind said she had run away from home. But decades after the fact, Sarah began piecing together memories and evidence from her childhood that made her suspect something far more nefarious might be at play, with many signs, she claims, pointing to her father Michael Turney.

Sarah’s own investigation has become viral across her social media pages in recent years, sharing the story of her search for answers about her sister Alissa’s disappearance and her belief that her father, a retired sheriff’s deputy, had something to do with it.  (Alissa is presumed dead, but her body has never been found.)

“Back then, I was oblivious,” Sarah says in a clip shared with PEOPLE. “All I knew was my dad's word and so his word was law.”

Alissa was 17 when she disappeared, and Sarah was 12. Their father Michael filed a missing persons report the night Alissa went missing, and Phoenix police originally concluded that she ran away from home.

But pressure from Sarah and her five siblings, who all believe their father was responsible for Alissa’s disappearance, ultimately led to a closer look. In recent years, Sarah has launched a podcast, a Facebook group, an Instagram account and later a TikTok account airing details about her sister’s relationship with their father. Sarah also penned an online petition calling for a murder trial against her father, which gained nearly 300,000 signatures and eventually landed the Turney family in court.

Michael was charged with second-degree murder in 2020 but was acquitted in 2023 after a judge said there was a lack of evidence, PEOPLE previously reported.

Sarah says her father, who was Alissa’s stepfather, “would constantly talk about how Alissa was going around the neighborhood and blabbing our secrets to everyone, telling ‘our family secrets.’ That's a phrase I always heard growing up.”

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In Family Secrets, Sarah says she believes her father “was terrified” that Alissa was becoming more independent in her late teenage years, “so he controlled every aspect of her life by design.” During the documentary, Sarah points to a trove of suspicious events she claims happened during her childhood – from her father allegedly placing video cameras in the vents that enabled him to look at Alissa, to presenting her friends’ parents with legal contracts after they invited her over to their house.

“He wanted to make sure that she was only engaging in activities that he felt appropriate for her,” Sarah says in the new trailer, adding about the contract, “It was a little odd and off-putting.”

For his part, Michael has proclaimed his innocence in connection with Alissa's disappearance, and he told ABC's 20/20 that the surveillance cameras he'd set up were for security purposes.