SOUTH KINGSTOWN — Leaking grease caused a 2000 Subaru Forester in which a woman’s body was found to catch fire last week outside 86 Berry Hill Lane in Kingston, according to the fire marshal’s office.

“It was accidental,” said Michael Sweeney, chief of investigations with the office.

Firefighters found the body of Katherine C. Helweg, who lived at that address, inside the car after they put out the blaze around 5:40 p.m. on Dec. 11. The state medical examiner’s office might release a cause of death today, a spokeswoman said. Investigators concluded that the car had been running for a period of time before catching fire, Sweeney said.

A mechanic explained yesterday that grease can ignite if it leaks from the boot surrounding the axles onto the exhaust system. Sweeney associated any leak with normal wear and tear on a car that age.

“It’s certainly unusual,” he said, adding, “She should have gotten out of the vehicle but she became incapacitated and couldn’t get out.”

Helweg, 59, a special-education teacher in the Chariho school district, suffered from diabetes, according to the police.