Lara Reynolds, a senior at Life Christian Academy in Tacoma, was last seen Saturday after a party in Parkland.

Video: Shocking Discovery In Search For Teen

"She was leaving at 12:30 and a friend was supposed to be driving her home however, she decided she was going to go ahead and get in her car and she left the apartment complex and no one has seen her since," said her mother, Patti Reynolds, in an interview with KIRO 7 Eyewitness News Monday morning.

Lara's family and friends had printed flyers and were going door to door asking for information when Lara's car was found in the Stuck River in Sumner.

Divers discovered a body inside and police determined it was Lara's.

Detectives soon discovered evidence that her death might not be an accident.

"We're investigating it as a homicide," said Ed Troyer, of the Pierce County Sheriff's Office.

Troyer said the case is being treated as a homicide, not because of any hard evidence, but because Reynolds was a responsible person who always made curfew and was not known to have a reason to be in the area where the car was found, just outside the Sumner city limits.

Troyer said the car may have gone in the river elsewhere and drifted downstream to the site where it was spotted.

Formal identification will come from the medical examiner's office, Troyer said.