Firefighters extinguishing the blaze at the house in Boulevard, southeast of San Diego, found Christina Anderson dead inside, and investigators later determined the 44-year-old was the victim of a homicide, sheriff's officials said in a statement. They did not say how she was killed.
After the fire was out, authorities looking through a detached garage found another burned body - a child whose identity and manner of death remained undetermined, sheriff's officials said. They wouldn't say whether the body may have been one of Anderson's two children, Hannah, 16, and Ethan, 8.
A dog was also found dead inside the house.
An Amber Alert was issued Monday night for the two children, and officials said they may have been abducted by James Lee Dimaggio, 40.
DiMaggio, who owns the home and lives there alone, was in a "close platonic relationship" with Anderson, the sheriff's statement said without further explanation.
The Amber Alert said DiMaggio is believed to be driving a blue Nissan Versa with California license plates.