The death of a woman whose body was found in a wooded area of Ridley Creek State Park on Saturday has been ruled a suicide.

Teresa Cathleen Mastracola, 44, of Millbourne, died of "chemical asphyxia" from "helium inhalation," according to the report released Monday by the Delaware County Medical Examiner's Office.

State and local police declined to comment on the cause of death, but had indicated there was no sign of foul play.

Mastracola, who police said was a member of the National Guard and a technician at Delaware County Memorial Hospital, had been missing since Dec. 2. She was last seen wearing hospital scrubs.

She was described as an avid biker and hiker, and was said to have frequented the park.

As of late Monday, police said her car, a silver Mazda 6 with a black bicycle rack attached to the trunk, had still not been found.

Mastracola's body was discovered not far from a trail near a picnic area, authorities said.

Contact Rita Giordano at 610-627-2649, rgiordano@phillynews.com, or follow on Twitter @ritagiordano.