He was at work at the time and planned to head to his mother's birthday party afterward.
When his two children called a second time, this time after dark, he decided to return home.
"I went to the house and there wasn't anything out of place. Everything was right where it was supposed to be. I waited and waited. Around 8 o'clock or so, I called the police," he said.
An exhaustive investigation followed. For months, local, state and federal investigators interviewed dozens of family members, friends, neighbors and co-workers to no avail, said the Lititz Borough police news release.
Four days after she disappeared, Brenda Heist's car was found legally parked in a parking spot in a nearby city.
There was no damage to the car, but it was parked near a bus station.
When police scoured bus and airline schedules, they couldn't find any bookings for Brenda Heist, according to case details provided by the Monroe County Sheriff's Office.
Lee Heist even became a suspect, though he was eventually cleared.
"The police always asked me if I wanted to have an attorney present, I said 'No, I don't need one.' I gave them total access to the house, to the computer, whatever they needed. I wanted answers," Lee Heist said.
The investigation continued for several years.
Six years after Heist went missing, Lititz police invited the Lancaster County Major Crimes Unit to join them in conducting a cold case investigation.
Detectives from all over the county interviewed several old and new witnesses, poring over every bit of evidence collected during the original investigation, said the Lititz police news release.
"We couldn't overlook anything, so it went in many different directions. We would have calls every so often where somebody would say that they saw her. Many people became persons-of-interest," Schofield said.
"We'd get a call from someone who said she was buried in the woods, only to find out it was only a dirt mound when we went to investigate. Individuals were acting suspicious, calling saying they knew where she was. We'd just find out later that they were mentally unstable."
While police did find some new information, all of their leads came up short.
"I won't even get into the number of psychics who called in, saying they knew where she was. Obviously that didn't pan out," he said.
Despite years of dedicated investigation, it seemed like an answer to Heist's whereabouts would never be found.
Not without her children
Friends and family were convinced that something bad had happened to her.
While they couldn't determine how she disappeared, they all agreed on one thing: There was no way Heist would ever leave her children, or so they thought.
"When the investigation first began, after interviewing all of her family and friends, neighbors, co -workers, the one consistent thing they all said was that she would never leave on her own. She would never leave her children behind," said Schofield.
"The fact that she left on her own was one of the theories, but it was at the bottom of the list," he said.
In 2010, Lee Heist filed a petition with the county court to have Brenda declared legally deceased, according to the Lititz police news release. It was a measure necessary for closure, he said.
He later remarried.