TEMECULA, Calif. —  A teenager who survived a murder-suicide that wiped out her family placed a frantic 911 call before she knew that her brother was the killer.

"My dad and his girlfriend and her children and my brother. They're all beaten to death in the backyard," 15-year-old Danielle Blixt said as she screamed and sobbed during a 911 call to a Riverside County sheriff's emergency operator on Nov. 11.

"They're dead. I thought they were just kidding around. I thought it was a joke. It's not a joke. They're bloody and beaten to death," Danielle said.

"They're dead. My family is dead. What else do you want me to say? I don't know who did it, I don't know how it happened, all I know is that they're all dead!"

Investigators said Monday they concluded that Danielle's 17-year-old brother, Matthew, shot and killed their father, Jeffrey Blixt, 45. He also killed Blixt's girlfriend, Naomi Grangroth, 34, and her twin 15-year-old daughters, Narissa and Nikita Williams, before committing suicide.

All were shot in the head with the father's 9 mm semiautomatic handgun, which was found under Matthew's body in the backyard. The teenager left no suicide note and investigators said they did not know the motive for the killings.

The Blixt children lived with their mother in Desert Hot Springs and had gathered for a Sunday barbecue at their father's home in the Temeku Hills subdivision of Temecula, 75 miles southeast of Los Angeles.

The 911 call was released Tuesday by authorities. Danielle made the call while driving around in her father's pickup after seeing her family's bodies and taking the keys from her father's pocket.

"I had to get out of there, I couldn't be there," Danielle tells the operator.

Danielle says she had gotten angry with her father and gone to a bedroom and was talking on the telephone when she heard a loud noise and a scream from her father's girlfriend. She did not think anything was wrong, however.

"They were watching movies. I heard her scream. And I heard a loud noise but I thought because they were barbecuing or something. I mean, she's an outrageous person," Danielle says.

"It didn't seem like a big deal, you know, because she's a very loud person," she said.

But on leaving the room later, she found the bodies of the twins lying in the living room. At first, she thought they were sleeping.

"One of them, I think, is alive because she's shaking. ... And I tried to tell her to get up. And she won't get up," Danielle said. "And I don't want to touch her because I could make it worse for her. And I don't know what to do. I don't know what to do."

Later she told the operator: "One of the girls sounded like she was snoring, but she must have been trying to get air!"

She found the other bodies outside.

"And I tried to get my brother up and he wouldn't get up. And I tried to get my dad up and he wouldn't get up. So I searched for keys everywhere — I had to get out of there. I couldn't be there."

"Please ... I'm only 15. I can't do this ... this isn't fair," she said.

At the time, she was unaware that her brother was the killer, and told the operator: "He had so many problems in life, but he's a good person."