The longtime attorney for the family of Natalee Holloway says a possible plea deal this week is contingent on Joran van der Sloot disclosing new details about Hollway’s 2005 death in Aruba.

Van der Sloot is set to appear in federal court in Birmingham on Wednesday for a plea and sentencing hearing. He previously pleaded not guilty to extorting Beth Holloway, Natalee’s mother.

“It was conditioned upon Mr. van der Sloot revealing details of how Natalee died and how her body was disposed of,’’ lawyer John Q. Kelly told Today.

Authorities have not confirmed Kelly’s statements to NBC. An order filed Friday in the case remains sealed.

Read full coverage of the case here

Although van der Sloot, now 35, has long been suspected in the disappearance and death of the Mountain Brook High School graduate Holloway, then 18, while she was visiting Aruba in 2005, he has never been charged in connection to her death.

The plea hearing comes days before what would be Holloway’s 37th birthday.

However, federal authorities in Alabama contend that in 2010 van der Sloot exploited the fear of Holloway’s mother, Beth, that she would never find her daughter’s body or know what happened to her unless she paid him $250,000.

A federal grand jury in Birmingham indicted van der Sloot on June 30, 2010, on charges of wire fraud and extortion.

Van der Sloot remains held in the Shelby County Jail.

Van der Sloot on June 8 was extradited from Peru, where he is serving 28 years for the 2010 murder of college student Stephany Flores, to Alabama.

The following day, he made his initial appearance in court and pleaded not guilty to the wire fraud and extortion charges.

The case is being prosecuted by Lloyd Peeples, chief of the U.S. Attorney’s Criminal Division, and Assistant U.S. Attorney Catherine Crosby.

Prosecutors contend that van der Sloot told Holloway for an initial payment of $25,000, he would take the Holloway’s representative to the location of Natalee’s body.

Once the body was recovered and confirmed to be Natalee, he said, he would then collect the remaining $225,000.

The affidavit said Natalee Holloway died after Joran van der Sloot threw her to the ground when she attempted to stop him from leaving her.

The affidavit also says that his late father, Paulus van der Sloot, then helped him dispose of her body.

Van der Sloot told a representative for Beth Holloway that his father buried her remains in the gravel under the foundation of the single-story house.

He later admitted to the representative that he lied about the location of Natalee’s remains.