Michaela Garecht was kidnapped from a grocery store parking lot in Hayward in 1988. Despite a massive investigation, she has never been found.
Phillip Garrido was sentenced to 431 years to life in prison in June for abducting Dugard in 1991 and holding her captive for 18 years at his Antioch home. His wife Nancy was sentenced to 36 years to life in prison.
Shortly after Dugard was found two years ago, police searched the couple's compound for ties to Garecht but found nothing.
According to the Oakland Tribune, Hayward police investigators spent more than two hours with the Garridos last week.
The Garridos deny involvement in the case, but investigators plan to question them again.
The Associated Press contributed to this report.