The fire was reported just after 1 a.m. Friday at an apartment building at 150 N. Allesandro Street, near Latham Avenue.
The father, identified as 41-year-old Juan Moreno, initially escaped the blaze with his wife Christina, 11-year-old daughter Jaelyn and infant Cecily. However, he died after rushing back into the burning unit in an attempt to rescue two of his daughters who were still trapped in the fire, according to Lt. Jeff Davis of the Hemet Police Department.
The girls were identified by relatives as 12-year-old Maria and 4-year-old Janessa.
The family's 8-year-old son, Isaac, was rescued but suffered extensive injuries and was airlifted to UCI Medical Center in Orange. He died from his injuries Saturday, according to a GoFundMe page set up to pay for the family's funeral expenses.
Investigators scouring through the remains of the Moreno's scorched unit for clues were unable to find signs that there were smoke alarms in the home, according to Hemet Fire Chief Scott Brown.
"This tragedy underscores how quickly a fire can spread. Smoke alarms are a key part of a home fire escape plan,'' Brown said.
Investigators said witness statements were key in helping them determine the cause of the fire.
When police and fire personnel reached the location, more than three-quarters of the occupants of the 25-unit, two-story complex had already gotten out, Davis said.
The blaze was raging on the northeast corner of the structure, Davis said, and public safety officials were immediately directed to the location by a distressed woman. She told authorities that her husband grabbed their infant and 11-year-old daughter, carrying them to safety, then darted back into the burning building for the rest of his children.
A neighbor who said he knew the family and spoke with the father just hours before the blaze mourned the loss.
"He was that type of dad, he was going to do any and everything to protect his kids," Robert Prideaux said. "Right now, I don't know to cry or not to cry. My emotions are just going all over the place."
Firefighters found the three victims dead inside the apartment, Davis said.
A vigil and fundraiser for the Moreno family was scheduled for New Years Eve. The event will take place between 8 a.m. and noon at the My City Youth Center, 145 N. Tahquitz Ave.
Both the Murrieta and Hemet locations of So Cal Tacos and Beer are donating 25% of proceeds Saturday and Sunday to the Moreno family, according to the restaurant's Facebook page. Customers must mention the Moreno family in order for the donation to be applied to their bill.
Red Cross staff was assisting the complex's 40 displaced residents.
City News Service contributed to this report.