"(He) sounded excited, like he was about to win something," one representative from American Express insurance told the FBI.
Court documents also show that Giordano had previously taken out an insurance policy on Gardner for a trip in June. The policy, obtained by ABC News, is dated April 27 and was signed by Gardner on May 12, officially designating Giordano as her beneficiary and listing him as her "domestic partner."
Gardner later canceled on Giordano and went to New York with her roommate, Christina Jones, instead. Jones has previously told ABCNews that Giordano sent Gardner aggressive, harmful texts for her decision to bail on the trip and go to New York.
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The details of the insurance call emerged as lawyers for Giordano went to court today in an attempt to overturn a court ruling keeping him in jail for another 60 days while police investigate the disappearance of Gardner.
The judge rejected the request, ensuring that Giordano will remain in an Aruban jail cell for the next few weeks.
Giordano has not been formally charged with any crime, and no body or evidence linking Giordano to a murder has been found. Gardner disappeared on Aug. 2, halfway through a weeklong trip taken by the pair, who met on an online swinger's website.
Giordano submitted a second insurance policy on Gardner on July 30, the day before the trip, by mail and fax. An insurance agent who spoke with ABC News said that no one she's dealt with in the entire year has both mailed a hard copy of their policy and faxed it in, noting Girodano's urgency in getting the documents in before the trip.
The insurance policy on Gardner is dated July 27, and is initialed and signed by Gardner, though the beneficiary information is filled out in Giordano's handwriting. Giordano listed his mother as his beneficiary on the forms.
Giordano, who has maintained that Gardner was swept out to sea while the two were snorkeling together, contacted the insurance company four times in the days after Gardner vanished, and told one insurance representative the she was likely dead, according to the transcripts.
"It's, you know, most likely a drowning," Giordano said. He also said he was "going to stay down here until the body's found."
"I've got to extend my rental car and I just don't want to start incurring all these costs to find out I did it wrong," he told the representative.
One insurance agent who spoke with Giordano said he was so disturbed by the call that he went home and called police in Gardner's hometown of Frederick, Md., and in Aruba.
Giordano's attorney, Michael Lopez, told ABC News that he advised his client to call AmEx.
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Former FBI agent Brad Garrett said the policies are important, but cannot stand alone without other evidence to convict him.
"I think it's an important piece," Garrett said. "Does it make it pre-meditated? It only does from the context, do you have other things that add to it in addition to the life insurance policy? It's the totality of his behavior that's very troubling."
Giordano is being held in a nine foot jail cell in Aruba with three other men. There is no air conditioning, and temperatures can reach 100 degrees. Giordano alleged that he had been sleeping on a concrete floor for the first few days there, but Aruban authorities now say he has been given a mattress.