She went out laughing. Investigators have ruled the death of a missing Delaware County woman found Saturday in Ridley Creek State Park a suicide by helium inhalation. Police tell NBC10 they found evidence at the scene, and the confirmation came from an autopsy.Teresa Mastracola, 44, of Millbourne, Pa. was last seen on Dec. 3. Investigators say she was spotted leaving her home on Millbourne Avenue.Credit: Millbourne Police DepartmentMastracolaâ€™s family tells NBC10 she was an avid hiker and bicyclist who often frequented Ridley Creek State Park in Edgmont Township. On Saturday, police say they found Mastracola in a heavily wooded area in Ridley Creek State Park.On Monday, the Delaware County Medical Examiner ruled Mastracola's death a suicide. According to the examiner, she died from asphyxiation caused by helium inhalation.