(NewsNation) — Two former Colorado funeral home operators were sentenced Tuesday for dissecting corpses and selling body parts without permission, according to federal officials.

Megan Hess, 46, was sentenced to 20 years in prison, and her mother, Shirley Koch, 69, was sentenced to 15 years, according to a statement from the U.S. Attorney’s Office for the District of Colorado.

Hess pleaded guilty to defrauding relatives of the dead in July. She operated the funeral home, Sunset Mesa, and a body parts business, Donor Services, from the same building in Montrose, Colorado.

Hess’ 20-year term was the maximum allowed under law.

Koch also pleaded guilty to fraud. Court records show Koch’s central role was chopping up the bodies.

“Hess and Koch used their funeral home at times to essentially steal bodies and body parts using fraudulent and forged donor forms,” prosecutor Tim Neff said in a court filing. “Hess and Koch’s conduct caused immense emotional pain for the families and next of kin.”

In their filing, prosecutors said Hess dissected 560 corpses, and they stressed the “macabre nature” of the scheme, describing it as one of the most significant body parts cases in recent U.S. history.

“This is the most emotionally draining case I have ever experienced on the bench,” U.S. District Judge Christine M. Arguello said during the sentencing hearing in Grand Junction, Colorado.

According to their plea agreements, Hess and Koch would also ship bodies and body parts that tested positive for, or belonged to people who had died from, infectious diseases, including Hepatitis B and C, and HIV, after certifying to buyers that the remains were disease-free. 

The judge ordered that Hess and Koch be sent to prison immediately.

“The defendants’ conduct was horrific and morbid and driven by greed. They took advantage of numerous victims who were at their lowest point given the recent loss of a loved one. We hope these prison sentences will bring the victims’ family members some amount of peace as they move forward in the grieving process,” said U.S. Attorney Cole Finegan. “We sincerely hope this punishment deters like-minded fraudsters in the future.”

Twenty-six victims described their horror at discovering what had happened to their loved ones.

“Our sweet mother, they dismembered her,” selling her shoulders, knees and feet for profit, Erin Smith said. “We don’t even have a name for a crime this heinous.”

Tina Shanon, whose mother was dismembered against her will, told the court, “I’ve worn many masks to cover the pain. I’ll never be OK.”

It is illegal in the United States to sell organs such as hearts, kidneys and tendons for transplant; they must be donated. But selling body parts such as heads, arms and spines – which is what Hess did – for use in research or education is not regulated by federal law.

Reuters contributed to this report.