The mystery of how a 44-year-old Michigan woman died and lay mummified in her car for years before she was discovered in March 2014 remains unsolved, the Detroit Free Press reported.

Pia Farrenkopf's corpse was found mummified and stuck to the back seat of her green SUV inside her garage by repairmen sent to the Pontiac home after it foreclosed.

"It smelled like death," Charles Golf, a worker Trademark Property Solutions who found the body, told the Free Press.

Oakland County investigators determined she died in early 2009, which means Farrenkopf, described as a loner with few friends, was in the garage for at least five years. But a medical examiner was unable to determine a cause of death because her organs were too mummified to be evaluated.

Farrenkopf kept to herself all her life. She came from a large Catholic family of ten sisters and brothers, but even they said Farrenkopf for the most part was a stranger to them.

"Sometimes she would go, literally, for years without us hearing from her," Jean LeBlanc, her sister, told the Free Press. "And then all of a sudden, she'd show up, so nobody ever thought anything about it."

After high school- which Farrenkopf excelled at- she took classes at the University of Massachusetts Boston and another community college before dropping out and taking a job in Arkansas in the '90s.

There, she earned a comfortable salary as a banking software developer for a tech firm, a job that sent her around the world. Her one friend at the job, Joan Gill Strack, said it was normal for Farrenkopf to disappear for extended periods of time.

"We worked in the international division, so everybody in that department traveled a lot," she told the newspaper. "It wasn't unusual for people to be gone for a month and then come back for a week or two and then be gone for another month or two."

Farrenkopf's career eventually took her to Michigan. That's when she started exhibiting strange behavior- even strange for her.

In 2003, she tried starting her own fitness company in Texas. But it resulted in failure and several lawsuits accusing her of breaking her lease and not paying credit card bills, according to court records obtained by the Free Press.

Court records noted it was difficult to get in touch with the defendant.

Farrenkopf remained elusive over the next few years, falling behind on bills and resigning from her job at Fidelity National Information Services in 2008 after 23 years. The reasons for her leaving are not clear.

She made a last withdrawal of $1,500 from her bank account, which had over $87,000, on Feb. 25, 2009. Investigators don't know what happened to her between that time and the time she died.

In the meantime, all seemed normal at her home in Pontiac- except for the missing owner. Farrenkopf made it so payments for her mortgage and other bills were automatically withdrawn from her account. Neighbors told the newspaper they had not seen her for years but thought she moved. A neighbor who said Farrenkopf paid him to cut her grass continued doing so for years after not seeing her. 

It was only when her bank account dried up and workers arrived to make repairs to the foreclosed home that she was found.

Oakland County sheriffs also found $500 in cash, a near-empty wine bottle with no fingerprints and hundreds of unopened mail dating from 2005 to 2007 inside the SUV.

Though a key was in the ignition, death by carbon monoxide poisoning is unlikely because the gas tank was not empty, Dr. Bernardino Pacris, the Oakland County deputy medical examiner who performed the autopsy, told the Free Press.  

"There was no trauma to the body, so it only leads to a couple conclusions," Oakland County Sheiff Michael Bouchard told the newspaper. "Either it was a medical situation that led to her death or something self-induced."

Police combed over every inch of Farrenkopf's life to determine what happened, but the case is no longer considered a priority.

Though she can't prove it, Paula Logan, another sister, thinks Farrenkopf was murdered. Her behavior indicated she was afraid of something.

"There's got to be something there that somebody missed," Logan told the Free Press. "I just hope people don't give up."