Forty-Nine-year-old cases are difficult to solve; potential witnesses have died, evidence may be long-gone and initial investigators could be retired. For the families of missing persons, though, the fight for justice has no expiration date.

Hinckley’s younger sister, Sheryl Ann Tillinghast, was last seen on September 24, 1973, in Wassaic, New York, a small town on the New York-Connecticut border.

Sheryl, according to her family, left $150 in paychecks and all of her belongings at her apartment. Tillinghast hadn’t lived at home in nearly a year; she’d been sent to a reform school for girls after pleading guilty to marijuana possession. However, the reform school burned down, and Tillinghast was transferred to the Wassaic State School for Mental Defects.

“She graduated from that school, but because of her bad relationship with my mother, she decided she didn’t want to come home,” Hinckley explained. “She stayed up there in the Wassaic State School area, got an apartment nearby and worked at the school’s laundry.

Despite their strained relationship, Hinckley claims her mother became concerned when Tillinghast failed to appear at a planned family birthday party.

“My mother called the school to find out where she was. “Sheryl was an adult, and she didn’t have to come home if she didn’t want to,” Hinckley told Dateline. “My mom just assumed that was it and never looked into it further.”

Hinckley stated that due to family dynamics, none of her siblings questioned their mother’s actions and thus did not follow up with the police.

“She was very authoritarian toward us,” Hinckley said in an interview with Dateline. “My siblings were afraid to do anything other than what my mother said.”

There is, however, a distinction to be made between not actively searching for someone and not even reporting them as a missing person to the police.

“I knew my mother rarely spoke with Sheryl and they had their issues, but surely she’d reported her missing. “Surely the cops had been looking for her all along,” Hinckley reasoned. “I was only nine years old when she went missing, so I assumed for years that they were looking for her and would find her one day.”

Hinckley and her siblings discovered the unthinkable one day in 1998, 25 years after Tillinghast was last seen: Their sister had never been reported missing to the police.

“I was taken aback,” Hinckley told Dateline. “She was a 17-year-old girl who vanished into thin air, leaving behind her belongings. The school was responsible for calling the police. My mother should have fought for her from the moment she realised Sheryl was missing until she died.”

The unfortunate discovery occurred by chance.

“A sheriff in Chester County, New Hampshire, was investigating an unidentified female remains investigation,” New York State Police Senior Investigator Tom Crowley told Dateline. “The sheriff’s department in New Hampshire saw a civilian report [of Sheryl Ann Tillinghast] in New York and thought it might be a possible match.”

Senior Investigator Allen Dombrowski retired in 2012, and Investigator Crowley took over the case. Investigator Crowley stated that Investigator Dombrowski “had to contact all the agencies in this area and downstate where she was last seen, and he determined there hadn’t been any investigation at all – there was no missing persons report for Sheryl.”

Hinckley claims that it wasn’t just their mother who let Tillinghast down by failing to report her missing. She told Dateline that her sister had an after-care case worker who should have handled the situation as well.

“There were no missing posters. “There were no searches,” Hinckley said. “All of those adults let her down by failing to report her missing.”

However, by 1998, the damage done by not conducting an initial investigation was nearly impossible to reverse.

According to Investigator Crowley, despite her failure to report her child missing, Tillinghast’s mother was never suspected of having a role in her daughter’s disappearance. With few leads, members of the New York State Police intelligence unit combed through police databases to see if Tillinghast had even existed after the date she was last seen, according to investigation records.

“They examined her pay stubs, taxes, and social security number…” Crowley, the investigator, stated. “There was absolutely no activity.”

“He tried everything he could to find her,” Hinckley said. “Then he asked if my sister and I could provide DNA samples so they could compare our DNA to unidentified bodies they discovered.”

Despite the passage of time, Tillinghast’s case remains open, and she is still listed as a missing person on the New York State Police website.

“There were physical searches of her school with canine assets. “We also conducted numerous interviews,” Investigator Crowley told Dateline. While the searches yielded no results, he stated that the interviews helped establish what her life was like at the time she vanished: who she hung out with, what she was doing, and so on.

“There were reports she had a boyfriend at the time, but he is no longer alive,” said Investigator Crowley. “Obviously, we would have liked to interview him, [but] we are still looking for people who knew Sheryl who can help us piece together the puzzle.”

Both the investigators and the family believe that some of the puzzle pieces have already been assembled.

“We believe she is deceased, but the body could absolutely be out there,” Investigator Crowley told Dateline. “That is where our investigation is going. But any lead that comes in, we take that information and follow it through to the end.”

Hinckley agrees, but adds that she does not believe her sister left on her own volition.

“I had a feeling something terrible happened to her,” Hinckley said. “She would at least try to get in touch with her siblings, because she loved us very much. There’s no way she’d just left.”

Hinckley said Tillinghast often took on a lot of the caregiving because she was the third oldest of eight children.

“She was like a mother figure to us. “She was concerned about us and babysat us,” Hinckley told Dateline. “She was the one who would bake Christmas cookies with us at Christmas.”

Authorities say no suspects have been named in the case, but there could have been if Tillinghast had been reported missing at the time of her disappearance.

“As soon as you suspect that someone is missing and the circumstances are suspicious, you should contact the authorities. “It’s critical,” said Investigator Crowley. “You must not be afraid or hesitant to follow up. I tell everyone I deal with in these situations that they can tell us as many times as they want, as frequently as they want.”

Sheryl Ann Tillinghast would have turned 66 today. She stands 5’3″ tall, has brown hair, and brown eyes. Anyone with information about her whereabouts is asked to contact the New York State Police Tip Line at 1-866-723-3697.