(CNN) -- For years, the payments went out of the woman's bank account.
Nobody batted an eyelid. Bills were paid. And life went on as normal in the quiet neighborhood of Pontiac, Michigan.
Neighbors didn't notice anything unusual. The woman traveled a lot, they said, and kept to herself. One of them mowed her grass to keep things looking tidy.
At some point, her bank account ran dry. The bills stopped being paid.
After its warnings went unanswered, the bank holding the mortgage foreclosed on the house, a common occurrence in a region hit hard by economic woes.
Still, nobody noticed what had happened inside the house. Nobody wondered out loud what had become of the owner.
Not until this week, when a worker sent by the bank to repair a hole in the roof made a grisly discovery.
The woman's mummified body was sitting in the back seat of her car, parked in the garage. The key was halfway in the ignition.
Authorities say they believe the woman died at least five years ago. They're still trying to figure out what happened.
"I've been doing this 37 years. Never seen anything like this before," said Undersheriff Mike McCabe of Oakland County, just outside Detroit.
Rarely heard from
The woman, who the sheriff's office believes to be Pia Farrenkopf, paid her bills from her bank account through auto-pay, according to McCabe. If she were still alive, Oakland County Sheriff Michael Bouchard said, Farrenkopf would be 49 years old.
Neighbors said they didn't know much about the woman, describing her as of German descent.
"She really kept to herself. We never really heard anything from her," neighbor Caitlyn Talbot told CNN affiliate WXYZ.
Talbot said she wasn't aware of anyone having seen the woman, who traveled a lot, in about six years.
"She was probably there for a couple of days, then she'd leave for a week, then she'd come back. Then she'd leave for a month and come back," Talbot said.
McCabe says neighbors chalked up the woman's absences to her returning to Germany for long periods of time.
According to the sheriff, Farrenkopf's employer last saw her in September 2008.
Despite years without a living owner, the house was never broken into, Talbot said. And McCabe said one of the neighbors cut the grass for years.
Authorities told WXYZ that the house appears to have black mold inside, and that detectives entered the building Thursday wearing hazardous material suits.
Bouchard, the county sheriff, said Friday that there were few outward signs of anything awry. Her mail didn't pile up, since the post office was collecting it. And nothing inside in her home or car pointed to a cause of death.
"Nothing remarkable (was) found in the home," the sheriff said.
Cause of death undetermined
Police were dispatched to the house for a welfare check in 2007 after a neighbor reported not having seen the owner in a while. After seeing no signs of anything amiss, police went on their way, McCabe said.
While authorities believe the body is that of Farrenkopf, they will rely on dental records to positively identify her. Farrenkopf's estranged sister has been contacted, according to the undersheriff.
Authorities are awaiting for a toxicology report, which will take four to six weeks, before determining the cause of death. The medical examiner found no signs of trauma to the body, McCabe said.
Dr. Bernardino Pacris, the county deputy medical examiner who conducted the autopsy, told the Detroit Free Press that the woman's skin was still intact, but that the internal organs had decomposed.
Bouchard, the country sheriff, noted that her body was inside a closed vehicle inside a closed garage -- and, thus, not exposed to outside air or other factors that might contribute to decomposition.
Pacris told the newspaper that during the mummification process, skin develops a parchment-like consistency and leathery texture. Finding a body in such a condition is unusual, he said, but "once in a while, we see this."
CNN's Chris Welch contributed to this report.