An 8:20 p.m. call prompted officers to respond to a single-story house in the 3900 block of Bronson Avenue, where investigators determined that a homicide had occurred, according to the Los Angeles Police Department.
The caller was the son and grandson of the victims, whose bodies were found in the bathroom of the residence.
Investigators say the son of victim Paul White, 62, found him and his grandparents Orsie Carter, 77, and her husband William Carter, 82, dead in a bathroom Tuesday after 8 p.m.
Investigators say while all three victims suffered blunt force trauma, two of them also had gunshot wounds.
They believe whoever murdered the victims knew them because there was no forced entry into the home.
By Wednesday afternoon, police said they were seeking to question a person of interest in the case. By evening, they confirmed that they had detained her for questioning.
Investigators described 55-year-old Nancy Jackson as a person of interest in the case who had some type of relationship with the homeowner, who was one of the victims. She has not been placed under arrest.
Neighbors say they often saw Jackson with White over the last several months.