The remains were discovered in August by women cleaning an apartment building basement near MacArthur Park in Los Angeles.
The bodies were inside two leather doctor bags in a trunk that also contained ticket stubs from the 1932 Los Angeles Olympic Games.
"Coroner's investigators believe the two babies were brother and sister. One was a fetus, while the other appeared to be a full-term baby," a police statement said Monday. Exact ages were not determined.
Investigators could not determine when or how the children died. It was not known whether the mother miscarried or may have had abortions.
There were no signs of injury, and drug reports were inconclusive so the cause of death probably will never be known, the police statement said.
The trunk's owner was identified as Janet M. Barrie, a Scottish immigrant who was born in 1897 and worked as a nurse in Los Angeles before moving to Vancouver. Investigators linked the children to Barrie through a DNA sample from Barrie's niece, Marlene Brown of Alberta, Canada.
Barrie lived in the Westlake building for decades. She was a private live-in nurse for Mary Knapp, the wife of dentist George Knapp.
Barrie married Knapp after his wife died of breast cancer in 1964. He died four years later and she moved to Vancouver, where she died in 1994. Her ashes were placed in the same urn as the Knapp couple at Forest Lawn Memorial Park in Glendale.
Investigators were unable to find relatives of George Knapp to compare DNA and possibly determine the children's paternity. Voting records indicated Janet Barrie was living with the Knapps in the building as early as 1948.
John Holmes, 67, of Vancouver said it was possible his aunt bore the children while she was unmarried.
"The social stigma of having a child out of wedlock was different than it is today," he told the Los Angeles Times. "Maybe she just couldn't let go of the children. Maybe there was an attachment."
Holmes hopes the discovery won't tarnish his aunt's reputation.
"You don't know the real story behind the story, you know what I mean?" he said. "They were her babies, we know that. But everything else, you can only speculate."
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