Her family thought her death was a tragic accident. It was years before the truth came out.

Theresa Neubauer was at work five years ago at a Georgia university when she got a phone call that stunned her.

Her son-in-law — a prominent fertility doctor who’d authored or edited several medical books — had just been arrested on suspicion of murder in the mysterious death of her daughter, Susann Sills, 45.

Susann’s body had been found at the bottom of a staircase in the couple's suburban Southern California home in 2016.

Up until that April 2019 phone call, Neubauer said, her family hadn’t even known that authorities were investigating the death as suspicious. She’d viewed her daughter’s husband, Scott Sills, 59, as a man who’d lost his wife in a tragic accident, she said, and she viewed herself as his ally as he raised the couple’s twins on his own.

For more on the case, tune in to “If These Walls Could Talk” on “Dateline” at 9 ET/8 CT tonight.

“I thought the police were satisfied with the investigation — that he had nothing to do with it and he was this poor single father,” Neubauer told “Dateline” in her family’s first interview. 

“I hadn’t thought of him as a threat in any way,” she said. “It did not enter my mind.”

During Sills' murder trial last year, the prosecutor said there had been a violent struggle that ended with him strangling his wife and staging her body on the staircase. His lawyer attributed the death to an accidental fall.

Sills was convicted of second-degree murder and sentenced in March to 15 years to life in prison.

At the bottom of the stairs

On the morning of Nov. 16, 2016, Sills dialed 911 and said that he’d found his wife’s body at the bottom of the stairs in their home in San Clemente, roughly 60 miles south of Los Angeles. 

“I don’t have a pulse, and she’s cold,” he told the 911 operator, according to audio of the call.

Paramedics arrived minutes later, and Susann was pronounced dead at 6:35 a.m., her death certificate shows.

When Sills told his mother-in-law what happened in a phone call the next day, Neubauer recalled him saying that he’d heard a noise overnight but didn’t bother checking since the couple had two dogs and 12-year-old twins.

“There’s always noise in the house at night — somebody’s always doing something — so it didn’t concern him,” she recalled Sills saying. “But then in the morning, he found her downstairs.”

Sills told investigators from the Orange County Sheriff’s Department that he thought his wife’s death was a tragic result of migraine medication that may have caused her to lose her balance and tumble down the stairs, investigator Eric Hatch told “Dateline.”

Neubauer believed her daughter must’ve suffered a sudden and unexpected ailment — an aneurysm, perhaps — because she had always been especially agile and graceful. She’d done ballet and gymnastics as a child, Neubauer said, and as a teenager, she’d been a cheerleader and ran hurdles. 

As an adult, Susann — who helped her husband run their fertility clinic, the Center for Advanced Genetics — even made an audition video for the reality show “Survivor.”

“She never fell,” Neubauer said. “She didn’t even fall when she was a child.”

Neubauer said she wanted the detectives to know how “physically capable” her daughter was. When she related that information, she said, one of the investigators responded: “Yes, well, but accidents do happen.”

“Which, of course, is true,” Neubauer said. “I had no reason to think they would not have done a thorough investigation. So I thought it was done and it was over.”

Another investigator looking into the death, Dave Holloway, described their communication with the family as typical for a law enforcement investigation: sympathetic but limited. 

“We wouldn’t come right out and tell the family that it was definitely an accident,” he said. “We wouldn’t come out and say it was definitely a murder. We would tell them that we are conducting our investigation because at some point, we may need to ask them questions and we wouldn’t want to prejudice their answers.”

A fight, injuries and a topless photo

That meant Susann's relatives were unaware that investigators found possible evidence early on indicating that there could be more to her death than her husband’s theory suggested. 

In the bedroom where she had slept the night of her death, the detectives found hair and bloodstains on a curtain and baseboard, Hatch said. A preliminary autopsy showed that she suffered a considerable number of injuries, including what appeared to be defensive wounds on her arms and a ligature mark across her neck, he said.

Her husband also had an injury that the detectives found suspicious — a fresh-looking laceration on his head that he’d covered with a beanie, Hatch said. When detectives questioned Sills about it, Hatch recalled, he said it had happened while fixing his car a few days earlier. He denied knowing anything about the blood in the bedroom, Hatch said.

The investigators also found evidence that there may have been problems in the couple’s relationship. One of their children recalled his parents arguing the night of Susann’s death, Hatch said, and text messages showed her telling her husband that she was “trapped” and would “never be free.”

In Sills’ office, the detectives found a cryptic note — a message they later learned was linked to a bet Susann had made on a conservative website that Donald Trump would win the 2016 presidential election. 

When Trump won, Hatch said, Susann fulfilled her end of the bet and posted a topless photo of herself on the site. The message, which had been printed out and was sitting on Sills’ printer, was in response to her photo. 

“All I’ve got to say is you must have a super cool husband,” the message said.

“That told me that this posting had been on someone’s mind,” Holloway said. “That wasn’t something that just happened to be up there that day.”

When investigators asked Sills about the note, he denied printing it and said his wife had probably put it there. The argument was about his wife needing to get rest when she wasn’t feeling well, Hatch recalled Sills saying, and the texts were about finances in their business, according to his lawyer.

A long-awaited cause of death

Despite the detectives’ suspicions about Sills, the coroner was yet to determine the cause or manner of his wife's death. That process took a year.

Elise Hatcher, a former Orange County prosecutor who later handled the case, attributed the delay to the complexity of the woman’s injuries. With gunshots or stabbings, she told “Dateline,” the cause of death is clear and it’s far easier for prosecutors to file charges in those cases.

But with Susann, Hatcher said, the case couldn’t move forward until the coroner completed extensive testing looking at the ligature marks and her neck structure. 

“They’re very methodical,” Hatcher said. “In this case, it took a very long time.”

By November 2017, that testing was finally complete: Susann's death was a homicide, Hatch said. She’d been strangled with a ligature. 

Forensic testing showed that the blood in the bedroom belonged to both the dead woman and her husband, Holloway said. Stains on a shirt that Sills wore in the aftermath of his wife’s death that he attributed to chocolate milk were actually her blood, Holloway said, and his blood was found under her fingernails. 

While a toxicology analysis found pain medication in Susann's system, there didn’t appear to be enough to affect her balance, according to the report.

As the investigators worked

Susann’s relatives had no idea about the coroner’s findings. Nor was her mother aware of any problems in the couple’s relationship. Neubauer said she spoke with her daughter weekly, and the only issues Susann's related to her about her husband were minor.

“If there was a problem there, she never brought it up,” Neubauer said. “And she was not the meek kind of person.”

After Susann's death, Neubauer said, she’d remained in touch with Sills about the twins and found they worked well together. For a vacation to the Caribbean with his wife’s family, Sills updated the twins’ passports, filled out all the paperwork for diving classes and “seemed very happy about it,” she said.

“He did nothing to prevent them from coming out and being with us,” she said. 

For Sills, life continued as though he were not the subject of a homicide investigation.

Sympathetic neighbors said they organized prayers and meal drop-offs while Sills continued to raise their twins at the home where his wife died. He appeared on a Las Vegas radio show to discuss the dangers of a now-discontinued birth control device, and he worked on a new book, “Ovarian Reboot: A Personal Journey to Hormone & Fertility Renewal.”

The detectives, meanwhile, had returned to Sills and interviewed him again about the results from the coroner and the forensics testing. He was cooperative, Hatch said, but “he didn’t have an answer. He continued to deny that he had anything to do with Susann’s death — that it was an accident or she fell down the stairs.”

Although the investigation hadn’t uncovered a clear motive, investigators believed Sills was responsible in the murder of his wife and forwarded their findings to the Orange County District Attorney’s Office. Hatcher, the prosecutor assigned to the case, said that by the time she reviewed the two boxes of evidence, it had been roughly two years since Susann’s death.

“I felt very disturbed for the family and for Susann that it took so long to get to the bottom of it,” Hatcher said. “But by the time I reviewed it, there was enough there.”

Hatcher said she came to believe there had been a violent struggle in the bedroom where the blood was found. That struggle ended with Sills strangling his wife and staging her body on the stairs, she said. 

His lawyer, Jack Earley, maintained that Susann's death was from an accidental fall and said the ligature marks may have come from her dogs tightly pulling a scarf that had been found around her neck. 

On April 25, 2019, as Sills drove to work, undercover deputies pulled him over and arrested the doctor on suspicion of murder. 

Hatcher alerted Neubauer to the news, and five years later — after Covid-related delays — she was in court when her son-in-law went on trial. A jury convicted Sills of second-degree murder.

“Initially, there’s a moment of relief,” she said, recalling what it was like to hear the guilty verdict. “And then after that — but there’s no Susann. And there never will be.”