Exclusive: Man Behind the Van der Sloot Tapes

The man behind the undercover video in which Joran van der Sloot appears to admit he was present when Natalee Holloway died and that he helped dump her body in the ocean says he is "totally convinced Joran is telling the truth" on the tape.

Aruban investigators have traveled to the Netherlands to question van der Sloot after Dutch crime reporter Peter de Vries' explosive tape caused them to re-open the case.

"I am telling you honestly, I know what happened to that girl," van der Sloot told an associate of De Vries', Patrick Van der Eem, on the undercover video. He goes on to say that Holloway died in his arms and that he called a fried to dispose of her body.

"Joran is telling the truth about what happened to Natalee," De Vries told "Good Morning America" in an exclusive interview today, adding that "she died in his arms on the beach that night."

On the tape, van der Sloot told van der Eem that Holloway suffered a seizure during a romantic encounter between the pair, who had met hours before at a local nightclub.

At another point, he told van der Eem, "I tried to shake her. … I was shaking the bitch. I was like, 'What is wrong with you man?' I almost wanted to cry."

Van der Sloot said he feels lucky the police were not able to recover Holloway's body.

"I think I am incredibly lucky that she's never been found because if she had been found I would be in deep [excrement]," van der Sloot also said on the tape.

De Vries dismissed van der Sloot's claim that he was lying on the tape or that drugs affected his statement, saying "I don't buy these allegations."

Instead De Vries said the only question that remains is the identity of "Daury," the "really good friend" whom van der Sloot said he called from a pay phone and who helped him dispose of Holloway's body.

"Our insider was pushing him the next day [after the taped confession] a little bit on the name … and then he came up with 'Daury,' but the name he mentioned is not the Daury in the news," De Vries said.

Van der Sloot's attorney, Joe Tacopina, says there's evidence to suggest the pay phone call never happened. Tacopina says the Aruban Coast Guard checked the pay phone that Joran talked about on the tape and found no such call, which would apparently give credence to van der Sloot's claim that the story he told on the tape was a lie.

"The Aruban Coast Guard has already looked at that pay phone. There is no such call," said Tacopina.

But De Vries said Aruban investigators have told him it was not possible to for them to determine if the call was placed.

"I don't know how [Tacopina] knows this, because I had a telephone call a couple of months ago … saying it's impossible to say," De Vries said. "Maybe he is the same like his client and made some things up."

Aruban investigators have yet to publicly weigh in on recent developments in the case.

Some say that De Vries' methods, namely the fact that he used van der Eem to gain van der Sloot's confidence and videotaped him unknowingly, crossed a journalistic line. But he says he has no regrets.

"We did what we had to do, and what we accomplished is that the investigation is reopened and that Joran is again a suspect for homicide … Before this Joran considered himself as a winner," De Vries said.

Investigation Re-Opened

If van der Sloot's own words are to be believed — his fears about the body being found, and his calling a "really good friend" instead of an ambulance — then his story raises questions about the identity of his friend with the boat, Daury, and the possibility of that pay phone call.

ABC News' Elizabeth Vargas caught up with Daury Rodriguez, a 21-year-old Aruban man and longtime friend of van der Sloot's, in Aruba last week. Rodriguez denied that van der Sloot had called him or that he was with van der Sloot on the beach the night Holloway disappeared.

"So when Joran Van der Sloot said he had a friend, named Daury, who was here on the beach on May 29 2005, it wasn't you," Vargas asked him.

"No," Rodriguez replied. He also told Vargas that van der Sloot apologized and said he lied in an online conversation.

Today van der Sloot's family is reportedly concerned for his mental state, fearing that he may try to commit suicide.