Authorities responded to the 16000 block of East Janine Drive at 11:59 a.m. and found a woman shot to death. According to family members, the victim was identified as 60-year-old Debbie Escobedo.
Police said a family member made the discovery and called 911, telling authorities that the suspect may still be inside the home.
Police surrounded the residence seeking a possible suspect thought to be inside. SWAT team and homicide investigators were on scene. They entered the house about seven hours after surrounding the location.
Three people were found dead inside, including a man in his 30s, a man in his 60s and a woman in her 60s.
Escobedo had been living in the home for about 30 years, according to family members.
"I'm shocked because of the family that it is, a nice family," said neighbor Sonia Niebling.
Murphy Ranch Elementary School, with about 450 students, was locked down as a precaution. However, the children were released to their parents later in the afternoon.
The Associated Press contributed to this report.