(CNN) -- The man being detained in the case of a missing American woman in Aruba is no longer cooperating with authorities, an official in the Caribbean nation said Thursday.
Taco Stein, Aruba's solicitor general, said that Gary Giordano is claiming that it is within his rights not to talk.
This approach prompted Aruban authorities to change their tactics, including releasing the suspect's photo in an attempt to generate tips and requesting assistance from the FBI, said Stein.
Richard Wolf, an FBI spokesman in Baltimore, Maryland, confirmed Thursday that Aruban authorities have requested the U.S. agency's help. The assistance includes conducting interviews in the state, where 35-year-old Robyn Gardner lives.
Gardner was last seen August 2 near Baby Beach on the western tip of the Caribbean island, said Ann Angela, a spokeswoman for the Aruban prosecutor's office.
In a press release Thursday, the prosecutor's office continued to identify the 50-year-old American man "who was arrested as a suspect on August 5" by his initials, GVG. They also released a photo of the man, who appears to be Giordano.
Giordano's attorney Michael Lopez has not responded to calls from CNN. The lawyer has told reporters that his client is being held as a suspect in Gardner's death.
According to Aruban prosecutors, the missing woman and the suspect arrived on July 31 from the United States. Gardner's friend, Christina Jones, told HLN's Nancy Grace that the woman had known Giordano for "over a year" and flew to Aruba with him.
Jones said that she had some concerns about the trip, but Gardner "calmed me and said it was OK -- that the trip to Aruba was what she needed."
Giordano had told authorities that he had been snorkeling with Gardner behind Nanki Country Club when he signaled to her to swim back, according to a statement. When he reached the beach, the woman was nowhere to be found, the man allegedly said.
But no witnesses have come forward to say they saw Gardner and Giordano snorkeling off Baby Beach, Stein previously has said. Witnesses have said they saw the couple on the beach.
"The statements made by the traveling companion led to such questions that on Friday, August 5, 2011, it was decided to detain him for further questioning on the possible drowning of the woman," the prosecutor's office said.
Lopez, Giordano's attorney, said Tuesday his client came to Aruba on vacation with a female friend he had met on a dating site and has known for years.
Lopez earlier told reporters that his client had been cooperating with police. Lopez said that on his client's last scheduled day in Aruba, he asked authorities if he needed to stay.
"They didn't answer it, and on his way to the airport, they detained him as a suspect for murder," Lopez said.
Angela would not say what evidence led authorities to suspect his involvement in Gardner's disappearance.
After finding no trace of Gardner, authorities stopped their active search for her on Saturday and are now searching "passively," Angela said. Police helicopters and search and rescue officials are keeping their eyes out for any clues to her disappearance, "but it's not an active search anymore," she said.
The Aruban solicitor general's office said Thursday that "on short notice" it will formally request assistance from the U.S. Justice Department.Stein had said earlier that Aruban officials have had informal conversations with the FBI to verify information and would request help, including seeking telephone records and conducting background checks on both Gardner and Giordano.
Investigators in Aruba will analyze a rental car and electronic devices that were in Giordano's possession, Aruban officials said Wednesday.
Richard Forester, also of Maryland, told CNN he and Gardner have been dating for the past seven or eight months.
He told HLN's Nancy Grace on Wednesday evening that Gardner wasn't the type to go into deep water, and would more likely stay by the pool.
"It's just not her to go out and snorkel," Forester said.
Forester said Tuesday that before Gardner's trip, the two argued over "the circumstances of her travel" to Aruba. He last heard from her on August 2 in a Facebook message, in which she said they would "work it out" when she got back.
Earlier that day, Forester said, Gardner posted on her Facebook wall "this sucks," with no further explanation.
She was scheduled to return to the United States on August 4, Forester said.
In an interview with HLN's Jane Velez-Mitchell on Thursday -- the same day he was interviewed by authorities -- Forester described Gardner as a woman who "loved life."
"She loved to be happy, loved to have fun, loved to be active," he said. "She had a very loving, warm heart."
The Natalee Holloway Resource Center -- named after a young American woman whose disappearance in Aruba made international news -- said Forester brought their attention to the case Monday.
The Aruban public prosecutor's office, as well as Forester, urged people in the Caribbean, the United States and elsewhere to come forward with information about Giordano, Gardner and the case.
"It's very hard not knowing," Forester told HLN's Grace on Thursday. "I would ask everybody who knows anything about (Giordano) to come forward."
CNN's Martin Savidge and Josh Levs contributed to this report.