Updated 01/14/15 – 10:56 a.m.

(CBS) — Federal agents raided two suburban locations Tuesday. At one, investigators found a cache of documents and at the other, hundreds of body parts.

Sources tell CBS 2’s Brad Edwards that this is part of a national, year-long investigation. Previous reports and sources say at the core, the allegation that donated bodies may have ended up being body parts on the black market.

Agents with the FBI’s evidence response team raided Cremation Services Incorporated at 9329 Bryon Street, in Schiller Park. Sources tell Edwards that agents found “hundreds of body parts” and that “it’s a mess.”

Federal agents returned to the crematorium on Wednesday, and hauled away boxes of documents.

The second raid occurred at the Biological Resource Center of Illinois at 9501 West Devon Avenue in Rosemont. Late Tuesday afternoon, boxes of documents were hauled away from the fifth floor office.

One year ago, a story broke about body parts from hundreds of people being stored on ice, not embalmed, in a rundown warehouse on Detroit’s East Side. That was later connected to a Phoenix body donation program called the Biological Resource Center, the same name on the Rosemont office raided Tuesday.

Its website says: “Whole body donated to medical education and research can be a lasting and enduring gift to society.”

In return, one gets free cremated remains within 30 days.

FBI confirms the dual searches and that it’s part of an on-going criminal investigation.

Brad Edwards