The death of the missing Delaware County woman found in Ridley Creek State Park over the weekend has been ruled a suicide.

The Delaware County Medical Examiner's Office has determined that Teresa Cathy Mastracola, who was found dead in an heavily wooded area in the park on Saturday, died of asphyxiation by helium inhalation, according to the Delaware County Daily Times.

Mastracola, 44, of Millbourne, had been missing since Dec. 2 and was known to frequent the park as an avid biker and hiker.

According to the Delco Times, Mastracola was last seen alive on surveillance video from Delaware County Memorial Hospital, where she worked. The video showed her arriving at work, but then leaving 10 minutes later.

Police are still searching for Mastracola's vehicle, a silver 2006 Mazda 6, four-door sedan with Pennsylvania Tag DTA-5563 and with a black bike rack attached.

Anyone with information regarding the location of the vehicle is asked to contact Millbourne Police at 610-352-1450 or State Police at 484-840-1000.