Burdick did not say what, specifically, Crews and Hoehn are accused of doing, but investigators say they believe the two, who live in the apartment where the infant was found, were probably the last ones to see Lafontaine-Greywind.
On Thursday, police found a newborn baby inside that neighbor's apartment.
The couple accused of killing Savanna LaFontaine-Greywind allegedly provided police with conflicting stories about how they ended up with the missing woman's baby.
Not long after LaFontaine-Greywind disappeared that Saturday, Greywind says she went straight upstairs, to the apartment shared by Brooke Lynn Crews, 38, and 32-year-old William Henry Hoehn, the pair later charged in the case. She was visiting Brooke Lynn Crews and William Henry Hoehn for a "sewing project".
An autopsy has not yet been performed, but it appears that Greywind was not pregnant when she died.
Additional charges against Hoehn and Crews are reportedly pending.
"As law enforcement, through our investigative efforts, we will continue to pursue justice for Savanna", said Chief Dave Todd, Fargo Police. Hoehn says Crews presented him with an infant baby girl and said: "This is our baby". Authorities recovered her body from the Red River on Sunday night, three days after finding a newborn they believe to be hers.
It's alleged this happened an hour after Ms Lafontaine-Greywind visited.
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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".
Police are still trying to determine whether the newborn is Savanna's, but they are nearly certain it is.
Greywind's boyfriend and father to her baby, Ashton Matheny, told Forum News Service last week his girlfriend's death breaks his heart.
An abandoned farmstead was also being searched in neighboring Clay County, Minnesota, after suspicious items found there by property owners indicated it might be a crime scene, Todd said.
At a news conference Friday, Todd said authorities were investigating a number of possible scenarios in Greywind's disappearance, including whether her child was removed from her womb or if labor had been induced.
"Both (of them) invoked their right to counsel and refused to answer any more questions", Todd said.
Greywind's body was found on Sunday, wrapped in plastic in a river.
The condition of Savanna LaFontaine-Greywind has not been addressed by police as of this writing.