Police and paramedics were called to a home in the 20000 block of Via Galileo around 3:50 p.m. on initial reports of three male patients who were reported dead at scene.
Shattered glass could be seen in a door leading to a backyard. A person was seen sitting in front of the home wrapped in a blanket and appearing visibly distressed.
Police said they are investigating the incident as a burglary homicide.
"At this time, it looks like someone entered the residence and there were some shots fired. There are multiple victims of gunshot wounds down inside of the residence and we do not have any suspect information that is available at this time," authorities said.
Investigators roped off the home located in the Renaissance development.
Neighbors in the gated community include Congressman Brad Sherman, who said he was out having dinner when the incident happened.
"Things can happen anywhere and at the same time, I think it's a very safe neighborhood," he said.
Authorities said they are looking for any witnesses who may have more information on the crime.