July 17 ,2013 , 2013 -- Authorities are still investigating what led to a St. Louis woman's death after her decomposing body was discovered slumped in the back seat of an unmarked police car.

The body of Leslie Wehmer, 41, was found by a Breckenridge Hills, Mo., traffic officer as he stopped by the vehicle just before the start of his shift on Monday. Wehmer had been reported missing Saturday after she left her home while intoxicated.

"Her family said that on Thursday night going into Friday that she and her boyfriend got into [an] argument," Breckenridge Hills Police Chief Perry Hopkins told ABCNews.com. "There was alcohol involved, and she ended up walking away from home. No one heard from her. Her family started to get a little bit concerned, though they said it was not highly unusual for her to disappear."

The family initially contacted the St. Louis police, concerned that Wehmer had crossed over nearby Cold Water Creek while intoxicated. But when police searched the creek they found nothing, Hopkins said.

It wasn't until Monday that the officer happened to come across her body in a state of decomposition. At that point, according to Hopkins, police went through the car, photographed the scene, and the medical examiner took her body to perform an autopsy.

Authorities will have no cause of death until they receive a toxicology report, but foul play has been ruled out, Hopkins said. Until then authorities can only speculate as to how Wehmer wound up in the unmarked car, which he said was accidentally left unlocked at the time.

"The hypothesis is … based on deceased woman, what the family knows, and the medical examiner's determination, that she probably left the house Friday morning, went from car to car looking for shelter, found our police car, crawled into it, passed out, and the next day when the temperature rose, she suffered a heat stroke and passed away," Hopkins told ABCNews.com.

Wehmer also suffered from epilepsy, and had several epileptic fits in the 12-hour period before she disappeared, Hopkins said members of her family told authorities.

Dave Childs, Wehmer's boyfriend, said that she often wandered off but returned home or called within a few days, according to the St. Louis Post-Dispatch. He also said that Wehmer had nerve damage from drinking and couldn't have walked as far as the police department.

Calls placed to Childs by ABCNews.com were not immediately returned. Image of Wehmer porvided by Fox station KTVI.