It started as a routine call for medical attention at an Ontario home early Saturday morning. But with a series of terrifying twists _ a husband with gunshot wounds, a wife firing on arriving police, a five-hour hostage standoff _ the call for help revealed a domestic tragedy.

Just after dawn, SWAT officers forced their way into the home on East F Street and discovered the bodies of the woman who had shot at police, a teenage girl and an elementary school-age boy, police said.

Police did not identify the deceased, but said the woman was an off-duty San Bernardino County probation officer. Her husband, who escaped the home when police arrived, is being treated for life-threatening injuries. "We don't have anybody to confirm identities yet," said Ontario police Sgt. Bill Russell.

"The husband is in the hospital and everybody else is deceased. So nobody has been able to shed light on what happened."

Investigators from the department and the coroner's office were in the home Saturday hunting for answers to a host of questions: Who died first? Who shot whom? How are the children related to the adults? And, perhaps most difficult of all, why did this happen?

Russell said detectives were in contact with relatives of the couple and were also looking into whether there had been previous requests for aide at the residence. The incident began shortly after 2:30 a.m. when the husband called 911. He indicated that someone was hurt in the home, but didn't say anything about being shot himself, Russell said.

Officers went to the home with firefighters prepared to provide medical treatment. When they knocked on the door, the man answered and walked outside. It was clear he had been shot and officers looking through the doorway could see his wife holding a gun. Russell said it was not clear whether officers or the woman fired first, but at some point she did shoot at them before barricading herself in the home.

"She ... pretty much ceased all communication at that point," Russell said.

Police learned that two children were possibly also in the house and called in SWAT and hostage negotiators. About 40 law enforcement officers descended on the neighborhood, a quiet area of single-family homes near a junior high, and nearby residences were evacuated while negotiators worked to establish contact with the woman. After about five hours without success, police entered the home and found the bodies, Russell said.

A spokeswoman for the probation department said she was still in the process of being briefed and had no immediate comment.