A mother and her adult son were found dead in the woman's home in Pico Rivera, according to the L.A. County Sheriff's Department.
The killings allegedly happened on a property on the 8900 block of Gallatin Road. Sheriff's deputies found the bodies of a man and a woman at about 11:30 p.m. Saturday.
"Family members became concerned about the mother at the home, as well as another brother, and came back and made the discovery of their bodies -- not inside the home but in a detached garage," Los Angeles County Sheriff's Sgt. Don Walls. "The bodies were concealed. They were not in plain view."
Detectives arrested a man they believe may have stabbed his mother and bludgeoned his brother to death.
The woman was identifed as 78-year-old Martha Garcia. Jorge Garcia, 52, sustained fatal blunt force trauma wounds. Autopsies were scheduled for Monday.
Authorities said a third victim, another brother, survived the attack and dialed 911. He was treated for undisclosed injuries.
The suspect was charged with suspicion of assault with a deadly weapon.
City News Service contributed to this report.