The man wanted for questioning is 33-year-old Ryan Michael Venti, the son of the couple who were found dead.
Authorities said they are looking for Venti, who they believe has mental health problems. They want to find him and speak with him about what may have happened at the home.
Venti was not at home at the time of the fire and has not returned.
He is described as having red/brown hair, blue eyes, weighing 180 lbs. and 6 feet tall.
RELATED: Homicide investigation underway after 2 people, dog found dead inside Diamond Bar home after fire
Homicide investigation underway after 2 people, dog found dead inside Diamond Bar home after fire
Detectives confirmed the identity of the victims as Linda Venti, 66, and John Venti, 75.
Firefighters received a call about the house fire around 4:44 a.m. Friday in the 3600 block of Crooked Creek Drive. It took crews a little more than 30 minutes to knock down the blaze.
When firefighters searched the home, two people and the dog were found. Sheriff's officials then arrived and determined it was a homicide.
Authorities said the victims were an elderly couple who lived with Ryan Venti.
The cause of the fire is under investigation, but authorities said some type of accelerant - possibly gasoline - may have started the blaze.