Giordano, 50, who met 35-year-old Gardner on a swinger's website a year before they decided to go on vacation to Aruba together, told prosecutors that Gardner been swept out to sea in rough currents while the two were snorkeling one evening.
Prosecutors have said that Giordano's story doesn't add up, and Gardner's boyfriend indicated that he agrees.
"There isn't any sign of her at all, no clue of her, no trace of her whatsoever that we know about," he said. "I can't imagine it would take more than a half hour to get to Venezuela. So from 4:15 in the afternoon until six in the evening, there's an hour and 45 minutes before he comes back and finally tells somebody that she's missing."
Forester said he had relayed his suspicions to the FBI and Aruban authorities, who told him they would follow where the evidence leads.
"I think it's an option that needs to be looked at," Forester said. "I know that it happens in that part of the world. It happens all over the world, but it's pretty big in that world."
Taco Stein, Aruba's head prosecutor, told ABC News that he would not comment on the the claim, but that it "speaks for itself."
Forester said he and Gardner were planning to get married and he did not learn that she'd gone to Aruba with Giordano until after she vanished.
"The last message I got from her was 'I love you, we'll talk and sort things out when I get back,'" Forester said.
Forester said in previous interviews that during Gardner's trip to Aruba, they kept in touch through Blackberry text messages and emails from her iPad until the day of her disappearance, including one message, in particular, that raised his alarm.
"On Tuesday morning, the 2nd of August, at about two in the morning, she posted on my Facebook wall, 'this sucks,'" he said. "I tried to figure out what was going on, but she didn't really respond."
Forester said today he still believes Giordano should be held responsible for her disappearance.
"Where's Robyn? Where is she? You're the last one to see her," he said of Giordano. "Where'd she go? I believe that he being the last person to see her and be with her is responsible."