Joran van der Sloot's recent confession that he killed Alabama teenager Natalee Holloway in Aruba in 2005 was years in the making, after investigators compiled detailed case files and, more recently, got the blessing of Holloway's mother for a related plea deal.
Van der Sloot's confession was publicized in court documents last week, shortly after he pleaded guilty in an Alabama federal court to extorting and defrauding Holloway's family. The confession came in early October, authorities say.
"Going into that room that day, both parties kind of went in with a mutual understanding of why we were there and what we hoped to accomplish," an FBI official told CNN of the day they sat down with Holloway's killer and captured his confession.
Van der Sloot confessed to killing Holloway as part of a plea agreement in the extortion and fraud case. During his proffer, the Dutch national detailed how he killed Holloway, who was 18 at time, on a beach in Aruba after she rejected his sexual advances, eventually bludgeoning her with a cinder block and putting her body into the ocean, court documents show.
In a proffer, a defendant offers information that person knows about a crime, often as part of a plea deal.
"The Birmingham team of agents -- professional staff -- we did our homework. There was a lot of investigative work that was done over 18 years," the FBI official said. "We did a lot of preparation, a lot of reviewing of the case files, and what have you."
"His prior statements were reviewed by us, things that he had said or put out there in the media previously," the official continued. "We reviewed all of that hoping that we would get the opportunity to go into the plea agreement, proffer session, and be able to ask him direct questions."
In the weeks before the plea agreement finally came together, the FBI was also in contact with Holloway's mother, Beth, who has remained a fierce advocate for her daughter in the nearly 20 years since she went missing, the Holloway family attorney told CNN.
"She had a lot of input. She knew what was going on," John Q. Kelly told CNN. "They wanted her blessing before they finalized the plea deal."
"I've talked to Beth every day since (the sentencing)" Kelly said, "and she is exhaling. He had pled, it's basically over. There is some finality there."
Van der Sloot was brought to the US from Peru in June to face charges of extorting and defrauding Holloway's family as part of a plot to sell the family false information on where Holloway's remains were located, authorities said.
The Dutchman is serving a 28-year prison sentence in Peru after being convicted of murder in the 2010 death of Peruvian woman Stephany Flores. The 20-year sentence he received in the US on the extortion charges after the plea agreement will be served at the same time as his sentence in Peru.
Whether van der Sloot could face additional charges is not entirely clear. The statute of limitations for murder in Aruba -- 12 years -- has passed, but the Aruba prosecutor's office says that the case remains open and this month asked the US Department of Justice for documents pertaining to the investigation.
Aruban authorities will review and analyze the documents "before deciding on the procedural steps" to be taken against van der Sloot, a spokesperson for the Aruba prosecutor's office, Ann Angela, said.