A woman was detained in Tustin Wednesday on suspicion of killing her mother-in-law and transporting her remains after setting fire to a home in Diamond Bar hours earlier, authorities said.
The rapidly evolving case began about 1:30 a.m., when Los Angeles County firefighters were responding to a fire in the in the 1200 block of North Diamond Bar Boulevard, sheriff's Lt. Eddie Hernandez said.
No victims were found in the home, and there was no initial indication to county firefighters as to how it started, Hernandez said. Arson investigators were called to the blaze, he said.
Meanwhile, the Tustin Police Department learned that a woman who lived at the Diamond Bar home was headed toward the Orange County city, Hernandez said.
"The information was that this occupant may have started the fire intentionally and killed one of the (other) occupants, that she was headed to this area and, potentially, the remains of the victim were inside the vehicle," Hernandez said from the scene in Tustin.
The source of the information provided to Tustin police was not immediately clear.
The woman's white SUV was stuffed with bags, and evidence markers were placed around bags that seemed to have fallen out of the vehicle, video from the scene showed. The vehicle was stopped at Tustin Ranch Road and Greenway Drive.
The Orange County coroner's office planned to take custody of the vehicle to inspect "any potential human remains" inside, and investigators planned to search for weapons as well, Hernandez said.
As it was later removed from the scene, body parts were seen in the vehicle, a detective on scene later said.
The preliminary investigation indicated the victim was the mother-in-law and the killer was the daughter-in-law, the lieutenant said. The daughter-in-law was detained without incident.
Neither woman was identified.
The remains in the vehicle were thought to be those of the driver's mother-in-law, authorities said. The older woman died at the Diamond Bar home, according to an afternoon news release from the Los Angeles County Sheriff's Department.
Video from early Wednesday showed flames surging through the Diamond Bar home, and smoke pouring from the structure.
The Los Angeles County Sheriff’s Department was handling the investigation in both Diamond Bar and Tustin, sheriff's spokeswoman Nicole Nishida said.
KTLA's Jennifer Thang contributed to this article.