The body was later identified as Greywind and has been sent to Ramsey County, Minnesota for an autopsy.
Brooke Lynn Crews, 38, and her boyfriend, William Hoehn, 32, were charged in the death of Savanna Greywind, the eight-months pregnant neighbor who was last seen on August 19 in the couple's Fargo apartment.
They had previously been arrested when a two-day-old baby, believed to be Greywind's daughter, was found in their apartment.
The neighbour of a dead pregnant woman has confessed to USA police she attempted to keep the baby for herself. Police arrested the neighbors and charged them with conspiracy to commit kidnapping.
A cause of death has yet to be confirmed. The murder conspiracy charge carries a potential punishment of life in prison without parole.
Speaking in a video posted to the Fargo Police Department's Facebook page, Chief David Todd said the infant would be DNA tested to confirm it was Savannah's child.More news: Australia wobble badly after Bangladesh rally to post 260 in Mirpur
Lt. Nelson provided additional information about earlier searches of Hoehn and Crews' Fargo apartment.
Crews allegedly admitted she had taken advantage of Greywind in an attempt to obtain her child and possibly keep the child as her own, the station reports.
She then presented him with the infant saying, "this is our baby, this is our family".
On Monday, Fargo Police Chief Dave Todd said it's time to shift the focus of the case from recovery to justice.
I would like to acknowledge the profound sadness being felt within our metro area over the loss of Fargo resident Savanna LaFontaine-Greywind.
She would never return home.More news: Punches fly during bench-clearing Major League Baseball brawl
It was about 2:30 p.m., an hour after their neighbor Savanna LaFontaine-Greywind told her parents she was going to Hoehn's and Crews' apartment.
Investigators remain tight-lipped about what happened to LaFontaine-Greywind after she went to that apartment. Todd added the plastic-wrapped body was found "hung up on a log", Valley News Live reported.
Police are still trying to determine whether the newborn is Savanna's, but they are nearly certain it is.
"Both (of them) invoked their right to counsel and refused to answer any more questions", Todd said. A farmstead was being searched and suspicious items found there led authorities to believe it may be a crime scene.
She was taken to a hospital and is now in the custody of Cass County Social Services, authorities said.
That claim contradicted what Hoehn told police.More news: Pupils praised as GCSE results are released