BILLINGS, Mont. (AP) — The death of a 16-year-old Hardin girl who went missing after reportedly walking away from a highway rest stop has been ruled accidental, Montana authorities said Saturday.

The ruling on Selena Not Afraid’s death by the Montana State Medical Examiner’s Office was released by the Big Horn County Sheriff’s Office, according to The Billings Gazette.

Not Afraid’s death will remain under review by the Montana Department of Justice’s Division of Criminal Investigation, the sheriff’s office statement said.

Not Afraid reportedly walked away from an Interstate 90 rest stop between Billings and Hardin on New Year’s Day. Her body was found 20 days later less than a mile away.

An autopsy found she died of hypothermia. She was not wearing adequate clothing for the cold weather, according to the missing person report issued on New Year’s Day.