By Molly Daly

MILLBOURNE, Pa. (CBS) — The Delaware County medical examiner’s office has ruled that Teresa Mastracola, the 44-year-old Millbourne woman whose body was found in Ridley Creek State Park, died by suicide.

The medical examiner’s report says Mastracola killed herself by inhaling helium.

Mastracola was last seen alive on December 2nd, when surveillance video from Delaware County Memorial Hospital showed her arriving at work early that morning, only to leave 10 minutes later (see previous story).

Her body was found Saturday in Ridley Creek State Park, where she frequently hiked and rode her bike.

Police have yet to find Mastracola’s car.