Aruban prosecutors asked the judge to keep prime suspect Gary Giordano locked up while they continue their investigation. This is the sixth time they asked to have his jail time extended.
However, on Friday the judge said no. He's ordering Giordano's release by Tuesday, with no conditions.
Giordano, a 50-year-old employment agency owner from Gaithersburg, Maryland, has spent nearly four months in custody while investigators have sought more time to gather and evaluate evidence in the death of Gardner.
Gardner, from Frederick, Maryland, is presumed dead but her body has not been found. Giordano has maintained that Gardner was swept out to sea while snorkeling on Aug. 2.
Prosecutors said they still consider Giordano a suspect. If he is freed and leaves Aruba, they would later request his extradition from the U.S. if they could find sufficient evidence to persuade a judge to order him rearrested.
The Associated Press contributed to this story.