"We have reasonable suspicion that this is the body of Nevaeh," Crutchfield said at a news conference.
The body was found Thursday under cement along the banks of the River Raisin in Monroe County's rural Raisinville Township, about 7 miles from Nevaeh's home in Monroe. Two fishermen found the cement and a shallow grave, said Andrew Arena, special agent in charge of the FBI's Detroit office.
It wasn't clear whether the cement was a slab or poured on the grave.
"It's a little more sophisticated than just dumping a body," Arena said.
Investigators hope autopsy and toxicology test results will confirm a cause of death. There were no obvious signs of violence to the body, Crutchfield said.
The body's discovery about 35 miles south of Detroit should allow investigators to focus on finding the person responsible, Crutchfield said. That person "to our knowledge is still out there in the community," he said.
When Nevaeh's mother, Jennifer Buchanan, was told about the body, "she broke down, and broke down hard," said Michael Buchanan, her brother.
"She couldn't believe her daughter had to go through this," he said, adding that if it is Nevaeh's body it provides "some type of closure, even if it is for the worst."
There have been no arrests in the case. Crutchfield wouldn't comment Friday when asked about two people previously identified as "persons of interest" in the case. One of them, George Kennedy, 39, is a friend of Nevaeh's mother and is a registered sex offender in custody on a parole violation.
A task force comprised of federal, state and local law enforcement agencies had been working 24 hours a day to find Nevaeh. Neighbors, friends and family members also combed the area.
The base of a large tree near Nevaeh's home has become a collection point for stuffed animals, pinwheels, a Pocahontas book and other items intended to honor Nevaeh.
"It hits home -- it really hits home," said Amanda Geiman-Martinez, who doesn't know the family but grew up nearby and now lives in Toledo, Ohio.
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