FBI agents raiding an Arizona body-donation center in 2014 were so traumatized by what they saw that some needed therapy, an agent has said.

Officials closed the Biological Resource Center (BRC) in Phoenix after an investigation into the misuse of bodies donated for scientific research in exchange for free cremation later on.

"Some individuals refused to go back into the scene," ex-FBI special agent Mark Cwynar told the Maricopa County superior court on Tuesday, adding that many needed therapy afterwards.

Cwynar said his team found a "cooler filled with male genitalia" and a woman's head sewn onto a man's body in a "Frankenstein" manner.

33 plaintiffs are suing BRC owner Stephen Gore, with some saying their relative's bodies were sold to the US military for blast tests without their consent.

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Some FBI agents raiding an Arizona body-donation center in January 2014 were so scarred by what they found they needed counseling afterwards, an agent who took part in the raid has told a court.

The Biological Resource Center (BRC) in Phoenix, Arizona, was shut down after an investigation into the misuse of dead body parts.

The for-profit facility took dead bodies from relatives on the pretense of using them for scientific research, in exchange giving the deceased's relatives a free cremation service later on.

"I personally observed several individuals emotionally upset. Some individuals refused to go back into the scene," Retired FBI special agent Mark Cwynar said of the raid at the Maricopa County superior court on Tuesday.

Cwynar said several agents required counseling in the aftermath of the raid