Authorities said the body of a small child found encased in cement near a Michigan river is the same size, age and gender of 5-year-old Nevaeh Buchanan and they have "reasonable suspicion" it is that of the missing girl.

An autopsy is being conducted on the little girl's remains, found by a father and son fishing along the banks of a river in southeast Michigan.

"The body appears to be of the same age, size and sex of Nevaeh Buchanan," Monroe County Sheriff Tilman Crutchfield told reporters Friday at a news conference. "We have reasonable suspicion that this is the body of Nevaeh."

The medical examiner's findings will confirm whether the body is that of the missing child, who last was seen May 24 in the parking lot of her apartment complex in nearby Monroe, Mich., about seven miles from the grisly find.

A shirt was found that resembles the one Nevaeh was wearing when she vanished, Crutchfield said.

The remains appeared to have been there for "quite some time," according to Crutchfield. He wouldn't discuss specifics on persons of interest or suspects in the case, but did describe the culprit as depraved.

"It is a very sick or disturbed person we are looking for," he 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 appeared to be buried in a shallow grave, said Andrew Arena, special agent in charge of the FBI's Detroit office. Investigators were returning to the river's edge Friday to look for more evidence.

The discovery of the body suspected to be Nevaeh 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 the girl'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."

The remains and other evidence were recovered from a shallow grave along the River Raisin's edge that had been covered with some kind of fast-drying cement powder, the Detroit Free Press reported early Friday.

Ryan Bickley, 15, told The Associated Press that his father, Guy Bickley, 51, discovered the body encased in cement Thursday morning while fishing the River Raisin.

The teen said his father and grandfather were fishing from shore when Guy Bickley spotted a block of poured cement and noticed a bad aroma that he likened to a decomposing body. He said as his father moved closer to the cement block, the smell "overwhelmed them."

His father then chipped away a piece of the cement, revealing what appeared to be human skin. The men immediately called police.

There have been no arrests in the case.

George Kennedy, 39, a registered sex offender, was one of at least two men previously identified by police as a "person of interest."

Kennedy told The Blade of Toledo, Ohio, in an interview published Thursday that he went to look for Buchanan after hearing from her mother that she had vanished.

Another man was cleared of involvement.

Kennedy is in custody on a parole violation. He is a friend of Nevaeh's mother.

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The Associated Press contributed to this report.