The body has been sent to Ramsey County in Minnesota for an autopsy.
Police found a newborn baby with Crews in the couple's apartment on Thursday.
Brooke Crews told cops she arranged to have Savanna Greywind, eight months pregnant at the time, come to her apartment in Fargo.
They are being held at the Cass County Jail and were scheduled to appear in court Monday afternoon to be formally charged with conspiracy to commit murder, conspiracy to commit kidnapping and giving false information, said Cass County State's Attorney Birch Burdick.
A cause of death has yet to be confirmed.
Police are still waiting for DNA confirmation that the child is Greywind's, but they say that the two suspects have already confirmed the baby is hers.
William Henry Hoehn and Brooke Lynne Crews are the two suspects in custody.
When she saw Crews' mugshot after the arrest, she felt a chill. Prosecutors have charged the man and woman who lived there with conspiracy to commit murder in what they say was a scheme to take Greywind's baby. Her body was found Sunday night in the Red River near Fargo.
Writing on Facebook, the Fargo Police Department said: "Over the last several days, we have devoted all of our investigative resources to complete the numerous investigative tasks associated with a missing person's case". There was no indication of LaFontaine-Greywind or a child during those three searches, Nelson said.
Ms Crews and Mr Hoehn during a court appearance via video link. Source AAP Cass County District Court
Experts had previously said it was possible Greywind was the victim of womb raiders, people who cut babies out of pregnant women to steal them. The suspects were Greywind's neighbors in the apartment building.
She would never return home. Her body was found in a river Sunday evening.
According to the complaint, Crews said she arranged to have Greywind come to her apartment on August 19 where she instructed her on "how to self-induce child birth by breaking her own water".
Authorities are still working to confirm that the newborn baby is Greywind's.
The infant, in the interim, is under perception at a healing facility in Fargo under the care of Cass County social administrations.
At a nearby farmstead, investigators found suspicious items that led them to believe it was a crime scene, Todd said.
"She loved everyone, she loved kids, her family - she would have been a wonderful mom", Greywind says.
The parents told of Savannah not taking her purse, not answering her phone with her vehicle remaining in the driveway.
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