Joran van der Sloot pleaded guilty to extortion and fraud last week in a twisted plot to con money out of the mother of Natalee Holloway, the Alabama teen he has now admitted to killing in Aruba in 2005.

While the plea deal in a federal court in Birmingham, Alabama, did not include murder charges for the slaying on foreign soil, authorities in both countries have indicated that criminal charges could still happen in the island nation.

Natalee Holloway was last seen alive on May 30, 2005, leaving a bar with van der Sloot. He was the prime suspect in her disappearance for the following 18 years and finally admitted to killing her in an Oct. 3 confession made public last week after he pleaded guilty to the extortion case.

JORAN VAN DER SLOOT’S WHIRLWIND PLEA DEAL: ‘HE WON THE GAME,’ BUT FAMILY ACCEPTS CLOSURE

Mugshot of Joran van der Sloot, the admitted killer of 18-year-old Alabama high schooler Natalee Holloway, taken in Alabama after Peruvian authorities agreed to send him to the U.S. to face trial in the middle of serving a sentence there for the murder of Stephany Flores. (Shelby County Jail)

The plea deal required van der Sloot to submit to a polygraph test – which he did. 

He accepted the deal, confessed to killing Holloway on the beach after she refused his sexual advances, and later passed a polygraph test. And he might have got away with it if the Holloway family, supporters, the FBI and an international team of investigators didn’t doggedly pursue the case for nearly two decades.

Beth Holloway, Natalee’s mother, told Fox News on Wednesday that in addition to the taped confession, the FBI has been able to corroborate his claims. And Judge Anna Manasco said in court that the confession was examined in combination with analysis and evidence by the FBI.

COURT RELEASES RECORDING OF JORAN VAN DER SLOOT’S NATALEE HOLLOWAY CONFESSION

WATCH: Beth Holloway believes Joran van der Sloot’s confession of murdering her daughter was ‘corroborated’

The polygraph was “just another tool” among many in a broader investigation, an FBI official told Fox News Digital Monday.

“We’ve been working on this case for 18 years, so there’s been a lot of investigative work done over that period of time that was a baseline of our investigation,” the official said.

Natalee Hollway, center, went missing during a spring break trip in 2005 and was never found. Last week, a federal court unsealed the confession of longtime suspect Joran van der Sloot, who admitted earlier this month to killing her on an Aruba beach when she refused his sexual advances. (FBI)

READ MORE ON NATALEE HOLLOWAY FROM FOX NEWS DIGITAL

The officials declined to go into specifics about the rest of that evidence, citing the potential that additional crimes could be under investigation by their counterparts in Aruba. But they said that the FBI, federal prosecutors – and importantly, the Holloway family – had all been satisfied that van der Sloot was being truthful in his recorded confession.

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“After 18 years, Natalee’s case has been solved,” Holloway’s mother told reporters outside the courthouse immediately after the hearing last week. “Joran van der Sloot is the killer.”

As part of the plea dal deal, Manasco said U.S. prosecutors have agreed not to use van der Sloot’s confession against him for any other purposes.

But in Aruba, authorities tell Fox News Digital that their case against van der Sloot is still open, and are requesting investigative documents from the Department of Justice.

“The Holloway case is still an open investigation in Aruba. The Police Force, the Public Prosecutor’s Office of Aruba and other investigative entities will follow up on any serious leads that could solve the disappearance of Natalee Holloway. The search of what happened to her remains unabated,” said Ann Angela, spokesperson for the Public Prosecutor’s Office of Aruba. “We have requested the U.S. Department of Justice for all the documents related to the investigation, which we will review before deciding on the procedural steps to be taken against Joran van der Sloot. Up until now, even though we are indeed aware of the reports in the press, we have not yet been formally informed by US authorities.”

However, Aruba has a 12-year statute of limitations for charging an individual with murder. Angela told Fox News Digital the issue isn’t cut-and-dry.

“Your question as to whether the suspicion against Joran van der Sloot, who at the time of the disappearance of Ms. Holloways was still a minor, is statute-barred or not, cannot be answered with a straightforward yes or no. It depends on various factors within the investigation. As it is an open investigation, the Public Prosecutor’s Office will only provide limited information to the media, also about the issue of the statute of limitation,” Angela said. “First things first for us at this moment in time, is to obtain the documents requested to the US Department of Justice.”

A man spits water on a poster of Joran van der Sloot outside San Pedro prison where van der Sloot stood trial fo the murder of Stephany Flores in 2012. The poster of Flores reads in Spanish “Stephany Flores asks for justice” and the poster of van der Sloot reads “Spiritual punishment.”  (AP Photo/Karel Navarro)

Van der Sloot will return to Peru to finish a sentence in the mountaintop Challapacla prison for the 2010 murder of Stephany Flores, a 21-year-old business student who he killed in her father’s casino. His sentence for the extortion and fraud charges will run concurrently, and once his Peruvian sentence is complete, he will remain imprisoned there for the remainder of his American punishment.

Van der Sloot’s lawyer previously told Fox News Digital his client hates the conditions there. Challapalca is known for its nighttime freezing temperatures, and van der Sloot was transferred there after a drug and cellphone smuggling scandal in his former prison. Challapalca is so remote and so high above sea level that there’s no cellphone service there, the lawyer said.

GRAPHIC: Read the transcript of Joran van der Sloot’s confession (Mobile users go here)

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Van der Sloot has offered shifting explanations for Holloway’s final hours over the years, including that he shoved her into a rock, causing a head injury. He has also claimed that his father, a prominent judge who died in 2010, helped hide the body.

In his confession, van der Sloot also said that two friends who were with him on the night of Holloway’s death had gone home before the murder.

A general view of the beach at the Marriott with the Holiday Inn resort visible in the distance, Noord, Aruba, Friday, May 12, 2023. The Holiday Inn resort is where Natalee Holloway stayed in 2005 before she disappeared. (Mega for Fox News Digital)

Satish and Deepak Kalpoe, along with van der Sloot, were arrested and released multiple times as Aruba authorities investigated the case. Island police also questioned Paulus van der Sloot, the killer’s father.

Holloway’s remains have not been found – however authorities haven’t ruled out that one day they may be.