When authorities entered Arthur Rathburn's warehouse in December 2013, it was "filthy," an FBI agent testified Friday as the body-parts broker's trial opened in a Detroit courtroom.

FBI agent Leslie Larsen and her colleagues found dead flies, dried blood on the floor -- plus human body parts in paint cans, beer coolers and plastic containers, she told the court.

Some body parts were found frozen together inside a refrigerator, next to ingredients for sandwiches, she said.

“We seized human remains, documents and tools,” Larsen testified, according to the Detroit Free Press.

"We seized human remains, documents and tools." — FBI agent Leslie Larsen

Authorities also allegedly found four fetuses preserved in liquid alongside human brain tissue, Reuters reported last month.

Rathburn, 64, is accused of selling diseased body parts. He faces 13 federal charges, including wire fraud, transport of hazardous material and making false statements to a public official, MLive reported.

He and his now ex-wife Elizabeth, were accused of fraud for misrepresenting the human body parts sold by their company, International Biological Inc.

However, Elizabeth pleaded guilty to one count of fraud, and has agreed to work with the government as a witness in her ex-husband’s case, the website reported.

Rathburn caught the eye of authorities after U.S. Customs agents seized a severed head he provided for a dental seminar while transporting it from Tel Aviv to Chicago.

The head was infected with sepsis, authorities said, and its packaging failed to meet shipping standards. It was packed in a trash bag in some fluid, inside a cooler, U.S. Attorney John Neal said during his opening statements, MLive reported.

Rathburn allegedly lied about the liquid, claiming it was mouth wash, and that he had embalmed the head, Neal said.

The defendant's attorney, James C. Howarth, argued that the case should not be a criminal matter, but merely a contractual dispute, MLive reported.

The trial is scheduled to resume Monday, with testimony expected to continue through early February, MLive reported.