The body was later identified as Greywind and has been sent to Ramsey County, Minnesota for an autopsy.
Savanna Greywind, 20, was eight-months pregnant when she left her family's apartment on August 19 to help an upstairs neighbor, according to television station KVRR in Fargo.
Officers took Crews and Hoehn in for questioning on Thursday after discovering a baby girl in the apartment they shared.
Savanna Greywind was eight-months pregnant when when she disappeared.
The Cass County State's Attorney says he plans to file Conspiracy to Commit Murder, Conspiracy to Commit Kidnapping and False Information charges against two people already arrested in connection with the disappearance of Savanna Greywind.
Crews, who lives in the apartment with 32-year-old William Henry Hoehn, told police Savanna had left after helping her with her dress.
William Hoehn and Brooke Crews were hit with charges in Savanna Greywind's death.
The two suspects, Crews and Hoehn, were formally charged on Monday, Aug. 28.
The body of 22-year-old Savanna LaFontaine-Greywind was found Sunday evening by kayakers.
Hoehn admitted to police that he helped remove garbage bags containing bloody towels and his own bloody shoes from the apartment and disposed of them in an apartment building dumpster in West Fargo, reports CBS affiliate KXJB-TV.
When she saw Crews' mugshot after the arrest, she felt a chill.
Fargo Police say they did not believe they would have been led to the scene through investigative channels, and credited those who volunteered to look for Greywind.
Crews had initially told police that Greywind gave up her baby before admitting to taking advantage of the woman in an attempt to get her baby. She claims Greywind returned to the apartment later and gave her the newborn.
Todd did not say whether there were signs of trauma to the body. Two recreational kayakers had come upon her body, which was wrapped in plastic and secured with duct tape.
While the details of the crime are still under investigation, it appears to be a case of what experts term "fetal abduction", when a baby is stolen from the womb of a pregnant mother.
Downstairs neighbor Rhonda Grimli told KARE 11 what she told police she heard that afternoon.
The infant, in the interim, is under perception at a healing facility in Fargo under the care of Cass County social administrations.