Authorities are now calling the deaths of two men and a woman found in a Fullerton home a triple homicide and said they also are trying to locate a 17-year-old girl who lived in the house.
Police had been called to the scene, a home in the 400 block of South Gilbert Street, early Saturday morning after another minor, a young girl, called dispatchers and said her parents had died.
Police received the child's call at 8:21 a.m. and the first officers arrived at 8:26 a.m.
Officers found a bizarre and unsettling scene: three bodies and two apparently untouched children. Police said the dead had suffered "significant trauma" but did not immediately release details, except to say no weapons were found at the scene.
"We have confirmed that we do not believe it is a murder-suicide," said Sgt. Jon Radus. "We are treating it as a triple homicide. We do not believe that this was a random act of violence."
A neighbor told a CBS Los Angeles reporter that the girl who made the call is a fourth-grader and that she has two older siblings.
The teenager being sought is Katlynn Goodwill Yost.
A police spokesman described her as "a missing/at-risk person." Officers have been looking for her since 9 a.m. Saturday morning.
"We're concerned about her welfare because she lives in a residence where three people were found deceased," Radus said.
Authorities described Katlynn as 5 feet 6, white, about 150 pounds, with strawberry blond hair and dark eyes.
Late Saturday evening, the Orange County coroner's office had not released the names of the dead, but police were in contact with extended family members of one or more of the victims, Radus said.
The names, ages and relationship of the three adults who were found dead are under investigation, Radus said.
Radus said that he believed the missing teenager and the girl who called police are related, but he did not confirm whether they are sisters.
"This is obviously a tragic event," Radus said. "The Fullerton Police Department has committed all its resources to identify who is responsible for committing this act."
Fullerton police are asking anyone with information to call detectives at (714) 738-6776. Callers wishing to remain anonymous can call Orange County Crime Stoppers at (855) TIP-OCCS ( 847-6627).
11:00 p.m.: This article was updated with the police announcement that they have concluded that the three deaths are a triple homicide.
9:55 p.m.: This article was updated with additional details from the investigation and the announcement that police are trying to locate a teenager who lived at the residence where three people were found dead.