Mary Opitz couldn't have been more than five minutes ahead of them, her mother Nancy Hoffman told Dateline.
But it only took those few minutes to change their family's lives forever.
"It's every single day. You think about it every single day. Those days have formed all these years now," Nancy told Dateline. "It's crazy to think about how long it's been."
It was January 16, 1981 when Nancy took her youngest daughter Mary, 17, and one of her sons to the Edison Mall in Fort Myers, Florida. They had a present to buy for a family friend.
"On our way out, I had run into someone I knew and we were talking. Mary didn't want to wait, so she said she'd meet us at the car. Her brother stayed with me," remembers Nancy.
"It couldn't have been more than five minutes until we got to the car, but Mary wasn't there."
The packages and bags Mary had been carrying were left on top of the car. There was no sign of what had happened or where she had gone. Nancy knew immediately something wasn't right.
"Did I think she just took off? Not at all," Nancy told Dateline.
Family members contacted police later that night, after several hours passed without word from Mary.
But they weren't taken seriously at first, according to Nancy. It was frustrating. She said police told her Mary was a teenager and perhaps she simply took off. It wouldn't be the first time that had happened, they said.
Nancy didn't buy that explanation, and kept pushing until the case ended up in the hands of the Lee County Sheriff's Office.
They've been investigating ever since.
Less than a month later, they had another case, unnervingly similar to Mary's.
On February 11, 1981, another teen, also named Mary, headed to the parking lot of the Edison Mall to pick up her mother from work. When Mary Hare's mother came outside, she discovered her daughter's vehicle parked and unlocked, according to newspaper reports from the time. Mary was nowhere to be found.
It would be four months before someone made the grisly discovery of Mary Hare's decomposing body in a ditch.
Both teens attended the same high school, and frequented the same restaurant where Mary Opitz worked as a dishwasher, her mother Nancy told Dateline. They were strikingly similar in appearance. It's unclear if they knew one another.
The eerie echoes of their cases still nag at Nancy.
"There had to be something going on at the time," she told Dateline. "We thought whoever got my daughter Mary maybe meant to get that other girl. Or someone had a certain look of who they wanted to grab. There are so many possibilities."
Authorities have never officially linked the two cases, but have said both girls could have been victims of suspected serial killer Christopher Wilder. Wilder was accused of sexually assaulting and murdering more than a dozen women in Florida and several other states during the early 1980s. He was killed during a shoot-out with police in 1984 after a six-week crime spree.
When asked if she believes Wilder had anything to do with her daughter's case, Nancy shrugs. "It's a possibility," she said. "But there are a lot of those."
The Lee County Sheriff's Office calls both Mary Optiz and Mary Hare's cases open and active, but few clues have surfaced.
A lot goes on in 36 years. Nancy is now a grandmother many times over. She's a great-grandmother of eight. She can't help but believe her daughter Mary is out there, somewhere, perhaps with kids of her own.
"I can't believe she's not out there," Nancy told Dateline. "Until they can prove to me differently -- to me she's alive. You have to keep hope alive, or else how could anyone cope with this situation?"
Nancy has kept the news clippings mentioning her daughter's story and has them in a folder. She's since moved away from Florida. Her other children, Nancy's siblings, are scattered across the country.
Answers would be nice after all these years, she told Dateline. "You have to keep living your life," Nancy said. "But you can't ever forget it. We all miss her dearly."
Anyone with information regarding Mary's case is urged to call the Lee County Sheriff's Office at (239) 477-1202.