A neighbor heard the shootings , but thought that it was a car accident.
"I heard a second bang and then I thought I saw a flash. I called my wife and she came out and a friend said 'Does that sound like gunshots to you?' We weren't sure so we decided to call 911," said Reggie Straughter, a neighbor.
Police say minutes later 14-year-old Ian Mercado, the sole survivor of the apparent murder-suicide, called 911 from their condo complex in Yorba Linda, a bedroom community about 40 miles southeast of Los Angeles.
"As officers were arriving an additional 911 phone call was received through our dispatch center. A 14-year-old stated that he and his brother had been shot," said Sgt. Peter Rodriguez, Brea Police Dept.
When officers arrived they found Maricel Cho, 39, dead on the front step. Her daughters Nicole Cho, 9, and Kathleen Cho, 8, were shot to death while they slept in their beds. Their younger brother Christopher, 5, was found dead in another bedroom along with his father's body on top of a shotgun.
Neighbor Richard Harris says that his daughter played with Kathleen, Nicole and Ian. He would also talk to the father on occasion while walking his dog.
"He seemed to me like a docile human being. He was very quiet. If I saw him when I walked by I would say hi and he would say hello back. He would stop and pet my dog. That would pretty much be it," said Richard Harris, a neighbor.
Investigators hope to interview the Ian Mercado, once he recovers from surgery for a gunshot wound to his torso.
The violence unfolded shortly before 11 p.m. Saturday. Authorities still are trying to determine a motive for the slayings.
Based on the number of shell casings found at the scene, investigators concluded that each victim was shot once.
The shooting rampage stunned police and residents of Yorba Linda, which is home to the Nixon Library and sits on the border of Orange and Riverside counties.
The teen gave police a brief statement at the scene, recounting what he told the 911 dispatcher. It appeared the boy was unaware his mother and sisters had also been shot, officials said.
On Sunday, coroner officials removed the bodies on a gurney draped in a red sheet while police searched the condo for evidence. Autopsies were planned for Monday.
A community meeting is being held at the Yorba Linda Educational Services Center at 499 Casa Loma in Yorba Linda on Monday at 7 p.m. The public is welcome.
A fund to benefit Ian Mercado has been set up at: Washington Mutual, 2500 E. Imperial Hwy, Suite 194 Brea 92821.
If you'd like to contribute, the account number is 3954785497.
For additional information, you may call the Washington Mutual (Imperial/Kraemer) Branch Manager Jean Veilleux at (714) 672-0130.