The courts in Aruba will likely accept the tape as evidence because it was recorded by a private citizen without any influence by authorities, Chief Prosecutor Hans Mos told reporters.
"I take it very seriously," Mos said of the video.
The tape, which was first broadcast Sunday on Dutch television, has appeared to spur the investigation: Mos said authorities in the Netherlands searched two homes Monday where Joran Van der Sloot has lived while attending college there.
A judge in Aruba denied a prosecution request to detain Van der Sloot based on the new information. Mos said they will file an appeal Tuesday and expect a decision within a week.
The prosecutor declined to provide any details about the searches. Bert de Rooij, a lawyer for Van der Sloot in the Netherlands, said police took a hard drive and a laptop.
De Rooij, speaking on Dutch television Monday, said the college student would make himself available for questioning by authorities if necessary. "As far as Joran is concerned, that can happen soon," he told the news program "Nova."
In the secret recordings, Van der Sloot said Holloway, 18, was drunk and that she began shaking and slumped down on the beach as they were kissing in May 2005.
"Suddenly she started shaking and then she didn't say anything," Van der Sloot said in Dutch, adding that he did not kill her. "I would never murder a girl."
He said he panicked and tried but failed to revive her. He said that Holloway looked dead but that he could not be sure she was not still alive when a friend took her away. Van der Sloot identified the friend only as "Daury."
Chris Lejeuz, an attorney for a 21-year-old man named Daury Rodriguez, who is an associate of Van der Sloot's, appeared with his client at a news conference in Oranjestad Monday and denied his client had any role in Holloway's death.
Mos said prosecutors believe Van der Sloot was telling the truth in the video because he seemed to struggle as he told the story and repeated it several times.
"Now, whether that is the truth, that has to be seen ..." he said. "Finally the court will have to decide whether this is a declaration ... that we can use as evidence in this court of law."
In the interview, Van der Sloot speaks to Patrick van der Eem, a 34-year-old Dutch businessman who told ABC News that he befriended the younger man with the intention of prying a confession out of him.
Van der Eem said he spent about two months getting to know Van der Sloot, regularly smoking marijuana together and playing poker late into the night, the businessman approached Dutch television crime reporter Peter R. de Vries, who rigged up a new Range Rover with secret cameras to capture their conversations.
"Why did I want this? It's obvious. Everybody was looking for the truth for (Holloway's) mother," he told ABC News, which planned to broadcast the interview on its "20/20" program Monday night. "I'm a father. I have two children, a girl six years old and a boy two years old."
Van der Eem, who grew up in the Caribbean, said he was angry with Van der Sloot for damaging the reputation of Aruba and the Netherlands.
Joseph Tacopina, a lawyer for Van der Sloot, said his client was not responsible for the Alabama teenager's death and that the tapes do not amount to a confession.
"There was no confession, no admission of a crime by Joran on any of these tapes, which is very telling," Tacopina said on ABC's "Good Morning America."
Last week, Van der Sloot said he was lying in those conversations and denied that he had anything to do with Holloway's disappearance. In the secret footage, Van der Sloot spoke with a man he believed to be his friend, who gave him "drugs, marijuana, things like that," Tacopina told ABC.
But Natalee's mother, Beth Twitty, told ABC: "I don't think any of us are surprised by his reaction (that his comments were fiction), but I know one thing. Once people see the video of Joran there are no more questions. There is no one who can walk away from this believing that he is innocent."
She said Van der Sloot didn't even know if her daughter was alive or not.
"Natalee never even had the chance for a medical doctor or a coroner, anyone, to determine (if she was alive)," Twitty said.
Holloway, of Mountain Brook, Ala., was last seen leaving a bar with Van der Sloot and two Surinamese brothers hours before she was due to board a flight home.
The three were arrested shortly after her disappearance and again in November, but released for lack of evidence. Prosecutors then dismissed their case against them, saying they lacked evidence even to prove a crime. All three have always denied any role in her disappearance.
