The identification was confirmed by dental records, police said Monday.
Steven Zelich, a former West Allis, Wis., police officer, was arrested last week on charges of hiding the corpses of Gamez and Laura Simonson, 37, of Farmington, Minn. He is being held in lieu of $1 million bail.
While investigators say Zelich admitted causing the deaths of both women, he has not yet been charged with homicide.
Zelich, 52, allegedly told police he met the woman now identified as Gamez on line and then arranged a face-to-face encounter in Kenosha, Wis. He said he kept the body in his home for a year before moving it to his car.
A road crew found the bodies earlier this month in Geneva, Wis.
Gamez's foster mother said she had been living with her foster father in Cottage Grove, Ore. Geneva Police Chief Steven Hurley said she was never officially reported missing.
Zelich had posted on a web forum catering to sadomasochists. Investigators said Gamez's hands were tied behind her back, while Zelich had been gagged.
"I think we leave that question wide open for right now," Walworth County Undersheriff Kurt Picknell said when asked if Zelich might be linked to other deaths.