ROBYN GARDNER’s mys­terious disappearance in Aruba may finally be solved with help from a woman who was busted having sex in a car with prime suspect GARY GIORDANO!

Authorities on the Caribbean is­land believe the woman may be able to shed light on what happened to blonde beauty Robyn, who vanished without a trace while on vacation with Giordano last year.

“It comes down to investigators wanting to know what Giordano may have told the woman,” a police in­sider in Aruba told The ENQUIRER. “They believe she may have heard things from him that will help po­lice finally discover what happened to Gardner. “

Giordano, 51, was arrested with Carol Ann Bock, 45, on May 18 after the pair were observed undressed and hav­ing sex in the back of Giordano’s Ca­dillac Escalade in a public parking ga­rage in Annapolis, Md.

The ENQUIRER had exclusively revealed that the kinky pair were ro­mantically involved in our March 19 issue.

“The Aruban police now want to talk with Ms. Bock,” confirmed a source close to island officials. “They believe Giordano may have con­fessed to her about Robyn’s murder or may have given her crucial infor­mation that would help lead them to her body.”

The goal of investigators is to get enough information to extra­dite Giordano to Aruba to face charges.

Giordano claims his swinger companion Robyn disappeared while they were snorkeling in Aruba on Aug. 2, 2011 – a story local authorities never believed. Not only did Robyn hate to swim, but if she had drowned, they be­lieve her body would have washed ashore. What’s more, Giordano took out a whopping $1.5 million insurance policy on Robyn and boldly tried to collect on it two days after she went missing.

“Aruban police firmly believe that Gary Giordano either mur­dered Ms. Gardner or knows more about what happened to her,” the close source told The ENQUIRER. “Carol Ann Bock may hold the key to putting him be­hind bars for life.”

Giordano and Bock were arrested by bicycle cops, who spotted the duo in the SUV. They had attempted to use a blanket to block windows, but several peo­ple observed them having sex.

“As I looked through the rear cargo-area window, I observed Ms. Bock lying mostly on her left side with her left breast exposed in plain sight,” the arrest report states. “Mr. Giordano was completely nude.”

Both were charged with indecent exposure, and a hearing has been set for Aug. 10. Now, Aruban authorities plan to ask the FBI to interview Bock about any information she may have about Robyn’s disappearance.

“If she provides new evidence,” said the police insider, “Aruban authorities could ask the FBI to arrest and extradite Gary Giordano since Robyn’s disappearance is still an open case.”