That autopsy, for 22-year-old Nadia Malik, was still pending the results of toxicology tests, investigators said.
Those results were expected to take six to eight weeks.
Her body was found in a car Thursday which had a number of parking tickets on the window.
Malik, of Marple Township in Delaware County, had been the subject of a multistate search since she was last seen on Feb. 9.
Malik's body showed no visible signs of trauma and was fully clothed, police said.
Police said the car was first ticketed on Feb. 10 a few blocks from the train station, and the car was towed to a spot behind the station on Valentine's Day because it was blocking snow removal. It was ticketed there a number of other times.
Police Lt. John Walker said it would have been difficult for officers issuing the parking tickets to see inside the car.
"If you look at the car, it's tinted heavily on the back and side windows, and the windshield would have been covered with snow," he said.
In addition, the passenger seat containing the body was completely reclined and the woman's head was covered with a black duffel bag, police said.
Someone outside the car "couldn't tell there was a body under the bag until you opened the car and grabbed the bag," Walker said.
Investigators say they want to question Malik's boyfriend, with whom she has two young children. He was arrested in Solon, Ohio, on a probation violation and is awaiting extradition but hasn't been charged in the case.