Federal prosecutors say Rathburn washed human remains down the drain, stored un-embalmed heads in mouthwash, and cremated torsos to provide the family but kept the rest of the body for later use.
Those new details surfaced in court filings that included statements from confidential sources that helped the FBI, including former employees, according to the Detroit Free Press.
Among other grisly details, prosecutors say Rathburn cut up bodies with chainsaws, shipped un-embalmed human heads in blood-filled coolers on commercial flights, and stored more than 1,000 body parts on ice at his warehouse in Detroit.
Last week, U.S. District Judge Paul D. Borman refused to keep the gruesome evidence against Rathburn out of an upcoming jury trial.
Rathburn and his wife ran International Biological Inc. in a rundown warehouse near the airport in Detroit, Michigan. Authorities say that between 2007 and 2013, he bought body parts with infectious diseases from suppliers in Arizona and Illinois and rented them to unsuspecting medical or dental researchers.
Those suppliers include Biological Resource Center of Illinois and Anatomical Service, Inc. Owners of both of those companies have been convicted on criminal charges of lying to family members about how donor bodies would be used and secretly selling them for profit.
Rathburn is also accused of renting out body parts that were never screened for infectious diseases. His estranged wife admitted taking human remains infected with HIV and hepatitis B to an anesthesiology conference in Washington, D.C. in 2012, claiming they were disease-free when she knew they were not.