Firefighters arrived on scene at about 2:20 a.m. in the 600 block of South Riverside Avenue to find heavy fire and smoke billowing from a downstairs apartment. One resident, a 74-year-old woman, was removed from the apartment before firefighters arrived. She was declared dead at the scene, but authorities determined that the woman had been killed before the start of the fire.
"Preliminary investigation reveals that the female was suffering from upper body trauma, so this investigation is now a homicide investigation, along with an arson investigation," said Rialto Police Capt. Randy D'Anda.
Detectives said a motive for the apparent murder was not known, but they were looking into the possibility that it may have been a robbery, and that the building was set on fire to cover up the crime.
Neighbors identified the woman as the manager of the apartment complex.
Authorities said the fire began in one apartment and spread to a second apartment, which sustained some damage as well. About 40 firefighters worked to knock down the fire in about 20 minutes.
The Red Cross was called in to help about 90 displaced residents. The city of Rialto placed some residents in the Johnson Community Center at 214 N. Palm Avenue. It was unclear when people would be allowed to return to their homes.
The cause of the fire was under investigation by the Rialto Fire Department and arson investigators.
Anyone with information was urged to call Rialto police at (909) 421-7227.