Gary Giordano, 51, was arrested in May in Annapolis. According to the arrest report, he was found naked with a woman in a sport-utility vehicle in a parking lot.
The case is not being prosecuted because prosecutors don't have the evidence needed to find him guilty of indecent exposure, said Kristin Fleckenstein, a spokeswoman for the Anne Arundel County State's Attorney's Office.
Giordano's lawyer, Steven Kupferburg, said that the evidence did not support the charge because the exposure wasn't "willful and intentional." He also said that the facts of the case were "not quite as clear" as they had been reported initially.
Giordano is suspected in the disappearance of Robyn Gardner, who was last seen one year ago in Aruba while the pair were vacationing. He was detained on the Caribbean island for several months but was released in November.