(Reuters) -Joran van der Sloot, the prime suspect in the 2005 death of Alabama teenager Natalee Holloway, admitted to killing her on a beach on the Caribbean island of Aruba, a confession he made in pleading guilty on Wednesday to charges of extorting the victim's mother.
In June, van der Sloot, 36, was temporarily extradited to Alabama from a Peruvian prison to face two U.S. charges of extortion and wire fraud. Since 2012, he has been serving a 28-year sentence for murdering another woman in Lima, Peru's capital.
He initially pleaded not guilty in federal court in Birmingham, Alabama, to charges that he had conspired to get Holloway's mother, Beth Holloway, to pay him $250,000 in 2010 in exchange for revealing the location of her daughter's remains.
"You are a killer and I want you to remember that every time that jail cell door slams," Beth Holloway said in court after van der Sloot entered his plea, NBC News reported.
In entering his guilty plea and waiving his right to appeal, van der Sloot apologized to the Holloway family and said he had embraced Christianity since the murder, NBC reported.
U.S. District Judge Anna Manasco sentenced him to 20 years in prison, to be served concurrently with his sentence in Peru, followed by three years of supervised release.
He is expected to soon be returned to Peru to complete his sentence there, with an order to return to the U.S. if he is paroled or released.
Holloway, an 18-year-old from a Birmingham suburb, went missing in 2005 during a high school graduation trip to the Caribbean island of Aruba, a territory of the Netherlands.
Eyewitnesses said she was last seen leaving a bar in a car with van der Sloot on the night of her disappearance. While her remains were never found, an Alabama judge declared her legally dead in 2012.
Earlier this month, as part of the plea deal on the extortion and wire fraud charges, van der Sloot confessed to U.S. investigators he had killed Holloway after she repeatedly rebuffed his sexual advances on a beach near her hotel. After she kneed him in his crotch, he said he kicked her in the face, knocking her unconscious, and then picked up a "huge cinder block" nearby.
"I smash her head in with it completely," he told investigators, according to a transcript filed with the court. He then dumped her body in the ocean and walked home, he said.
"Today marks the end of 18 years of wondering what happened to Natalee Holloway," U.S. Attorney Prim Escalona told reporters after the hearing.
Dutch authorities in Aruba arrested van der Sloot twice on suspicion of murder, but ultimately released him for lack of evidence.
Working with the FBI in a sting operation, Holloway's family wired a portion of the demanded money, $25,100, to van der Sloot in 2010, but he then provided false information about where Holloway's remains were buried.
In sentencing, Judge Manasco also ordered van der Sloot to pay $25,100 to Beth Holloway in restitution.
After the hearing, Beth Holloway said justice had been served.
"Van der Sloot's confession means we've finally reached the end of our never-ending nightmare," she told reporters. "Natalie's case is closed, as far as I'm concerned. It's over."
In 2012, van der Sloot was convicted in Peru after he confessed to beating, strangling and suffocating Stephany Flores, a 21-year-old Peruvian business student, in May 2010.
(Reporting by Jonathan Allen in New York; editing by Jonathan Oatis and Rod Nickel)