Holloway's mother said Van Der Sloot confessed to the murder as part of an extortion trial on Wednesday.
Joran van der Sloot admitted to killing Alabama teenager Natalee Holloway in Aruba in 2005, her mother said Wednesday, as he entered a plea deal with federal prosecutors in an extortion case stemming from the disappearance that received international attention.
"Joran van der Sloot is no longer the suspect in my daughter's murder," Holloway's mother Beth Holloway told reporters outside the federal courthouse in Birmingham, Alabama, after a plea and sentencing hearing for the 36-year-old Dutchman. "He is the killer."
Van der Sloot confessed to authorities that he killed Natalee Holloway while she was on a high school graduation trip, Beth Holloway said.
"He said that after killing her on the beach in Aruba, he put her into the water and that was the last that he ever saw her," she told reporters. "... I'm satisfied knowing that he did it, he did it alone and he disposed of her alone."
Holloway said Van der Sloot's confession was verified with a polygraph test. He hasn't been charged in the killing, and Beth Holloway said he couldn't be tried in the U.S. for it.
Van der Sloot pleaded guilty to extortion and wire fraud charges during Wednesday's hearing, and he was sentenced to 20 years in prison to run concurrently with his 28-year sentence in Peru in another killing. He was charged in 2010 with trying to extort a quarter-million dollars from Beth Holloway in exchange for information about her missing daughter's remains, but he wasn't extradited to the U.S. until earlier this year.
As part of the plea deal, an attorney for Beth Holloway said van der Sloot had to provide details about what happened to Natalee Holloway. Before U.S. District Judge Anna Manasco imposed her sentence, Beth Holloway told the court that van der Sloot had said he killed her daughter.
Were Natalee Holloway's remains ever found?
Holloway was legally declared dead in 2012. Her remains haven't been found. She was last seen with van der Sloot on the Caribbean island nation during the May 2005 trip.
The extortion case dates back to 2010, when Holloway had been missing for nearly five years. According to a grand jury indictment, van der Sloot contacted Beth Holloway's attorney John Q. Kelly and offered to give him details about how Natalee Holloway died and about the location of her remains in Aruba for an initial payment of $25,000.
In the next part of the scheme, when the remains were confirmed to be Holloway's, her mother would then pay van der Sloot an additional $225,000, according to the indictment.
Van der Sloot took Kelly to a site in Aruba, but after securing the initial $25,000 payment, van der Sloot said in an email that the information he provided was "worthless," according to the indictment.
In June, van der Sloot was extradited to the U.S. from Peru, where he has been serving incarcerated since he pleaded guilty in 2012 to killing 21-year-old college student Stephany Flores.
Beth Holloway said she was "overcome with mixed emotions" by van der Sloot's extradition.
"I am hopeful that some small semblance of justice may finally be realized, even though no act of justice will heal the pain we've endured," she said in a statement.
Natalee Holloway's father Dave Holloway called the extradition "an important step toward accountability and hopefully, justice."
U.S. Attorney Prim Escalona said van der Sloot would be returned to Peru after the case concludes.
This story originally published to CBS News on Oct. 18 at 12:37 p.m. PT.
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