A medical examiner was scheduled to perform an autopsy on 33-year-old Claudia Menjivar later in the day.
Yellow tape still cordons off the home in the 2100 block of Lupin Street where Menjivar was killed on Wednesday.
Simi Valley police say 35-year-old Jose Monteroso, the father of Menjivar's youngest child, is the sole suspect.
"There are obvious indications of blunt force trauma injury," said Lt. Stephanie Shannon of the Simi Valley Police Department.
Police say Menjivar lived in the house with her boyfriend and two children. Investigators reached Monteroso by phone and discovered he was driving around Simi Valley on Wednesday night. A negotiator was on the phone trying to get him to surrender at the police department, but to everyone's surprise, he returned to the crime scene.
Police moved onlookers out of the way and told them to take cover. Officers had their guns drawn as Monteroso was placed under arrest.
One neighbor shouted, "Let's hear it for Simi Valley police," and they cheered and clapped.
Frank Real, who lives across the street, said he was home when Menjivar's teenage daughter found her mother's body.
"I called 911 for the little girl that came out. She came out screaming," Real said.
Real said the couple had lived on Lupin Street for several years.
"I know the dad loved that kid a lot. It's kind of surprising to see it come to this," he said.
The last homicide in Simi Valley was just over a year ago. Neighbors say it's a quiet and safe street, and losing a neighbor in this way has stunned longtime residents.
"We were all really shocked actually," said neighbor Lupe Rico. "It's been years since something like this happened here, especially in Simi, so it's been really hard for all of us and for the kids."
Detectives plan to collect more evidence at the house and are awaiting a search warrant.
Menjivar's children are being cared for by family members.