(CNN) -- A Dutch man once considered a suspect in the 2005 disappearance of Alabama teenager Natalee Holloway has told a television station he dumped her body in a swamp, Aruba's chief prosecutor told CNN.
However, Joran van der Sloot's claims to Dutch station RTL-5 are "unbelievable," prosecutor Peter Blanken said.
RTL-5 said Tuesday it had "acquired exclusive material containing a statement by Joran van der Sloot" regarding Holloway's disappearance.
"This material was first offered to us in 2009," Remko van Westerloo, the station's director of programming, said in a statement.
"Obviously, our initial response was skeptical," van Westerloo said. "However, we did feel that this interview required thorough research. We've spoken to a variety of experts and several critics. These findings resulted in a TV special which will air this Sunday. It's up to the viewers to form their own opinions on the matter."
The statement did not divulge the contents of van der Sloot's interview. However, Blanken told CNN on Tuesday that van der Sloot says in the interview that he dumped Holloway's body "in a swamp on the north end of the island."
"He was very unspecific," Blanken said.
Blanken said RTL contacted him about the interview last summer, and the station showed the interview to him to get his reaction. He said his office and Aruban police investigated.
"We tried to verify it," Blanken said. "It couldn't be true. We talked with several witnesses and reviewed several facts. The story is unbelievable and not true, in my opinion."
He said his office told van der Sloot "we'd like him to come in and speak with us about it. He failed to respond."
Asked why van der Sloot gave the interview, Blanken said, "You should ask him. Maybe he wanted to be on camera or make some money."
Holloway was 18 when last seen in the early hours of May 30, 2005, leaving an Oranjestad, Aruba, nightclub with van der Sloot and two other men, brothers Deepak and Satish Kalpoe. She was visiting Aruba with about 100 classmates celebrating their graduation from Mountain Brook High School in suburban Birmingham, Alabama.
Holloway failed to show up for her flight home the following day, and her packed bags were found in her hotel room.
Van der Sloot and the Kalpoes were arrested and released in 2005 in connection with the case. In 2007, they were arrested a second time after Aruba's then-chief prosecutor, Hans Mos, said he had received new evidence in the case.
Van der Sloot, who was attending college in the Netherlands, was brought back to Aruba. But judges ruled the new evidence -- which included an Internet chat the same day Holloway disappeared with one of the three youths saying she was dead -- was not enough to keep them jailed.
In 2008, prosecutors sought unsuccessfully to arrest van der Sloot a third time after a videotape surfaced on Dutch television. In it, van der Sloot tells a man he considered to be his friend that he had sex with Holloway on the beach after leaving the nightclub, then she "started shaking" and lost consciousness. He said he panicked when he could not resuscitate her and called a friend who had a boat. The two put Holloway's body in the boat, he said, and then he went home. The friend told him the next day that he had carried the body out and dumped it in the ocean.
"I didn't lose a minute of sleep over it," van der Sloot said on the tape.
Holloway's mother, Beth Twitty, told ABC at the time that the video showed van der Sloot was "not innocent."
But an Aruba court ruled there was not enough evidence to re-arrest him. Aruban prosecutors said authorities had met with van der Sloot in the Netherlands, but in a two-hour interview he denied any role in Holloway's disappearance.
Van der Sloot acknowledged to a Dutch television program he made the comments, but said he was lying. "That is what he wanted to hear, so I told him what he wanted to hear," he said.
"When [van der Sloot] really wants to tell the truth, [we hope] he will," said Blanken, who took over as chief prosecutor in September. "He didn't tell the truth [this time]."
CNN's Susan Candiotti contributed to this report.