Skeletal remains of a man wearing a suit and tie were found sitting in a burial vault with no casket in sight at a historic black Illinois cemetery where workers allegedly dug up bodies and dumped them in a scheme to resell plots, officials said Friday.

Cook County Sheriff Tom Dart said detectives were exhuming that grave site and two others, including one where two burial vaults were stacked on top of each other — the first proof that the alleged plot involved burying bodies on already-occupied grave sites.

"An individual casket was removed and someone was put underneath inappropriately," Dart told reporters at the Burr Oak Cemetery. He said the original vault was taken out and buried again on top of a second vault unbeknownst to the family of the person whom records show is buried there.

Authorities believe they know the identity of one of the bodies but are unsure of the other, said Dart. Both bodies appeared to have been buried last year, he said.

The suburban Chicago cemetery is the final resting place of perhaps 100,000 people, including civil rights-era lynching victim Emmett Till, boxer Ezzard Charles and blues singers Dinah Washington and Willie Dixon. Authorities have said there is no evidence that any of those graves were tampered with.

Four workers were charged in the alleged scheme, which authorities say stretches back at least four years and netted $300,000. Investigators have received tens of thousands of complaints and requests for information from people with family members buried at the 150-acre cemetery.

Dart said authorities continue to find more bones and other evidence of the scheme. The skeletal remains of the man wearing a suit was discovered by a detective who spotted a hole in the ground and climbed inside a vault, he said.

As many as a dozen vaults — including one for an infant — also were found recently in a heavily wooded area after detectives removed brush and trees from the site, officials said.

Dart said more bones were found in a 4-5 feet-high mound of earth that appears to be man made.

"We've only done very, very shallow digging there and have found a substantial amount of bones," Dart said. "Just below that level is dead grass so it almost appears as if things were just dumped on top of existing grass."

Dart said investigators have also found destroyed or altered records that suggests the suspects were not keeping detailed notes about which graves were dug up and what was being done with remains.

Authorities say they believe at least 300 graves were dug up, and so far, more than 1,000 bones have been found.