The couple, Jon and Carie Hallford, operated the Return to Nature Funeral Home in Colorado Springs and Penrose, Colo.

They agreed to facing 15 to 20 years in prison after they each pleaded guilty in El Paso County Court to 191 felony counts of abuse of a corpse, Michael Allen, the district attorney for the 4th Judicial District of Colorado, said at a news conference. The Hallfords are scheduled to be sentenced in April on the state charges.

Return to Nature advertised to families that their loved ones would be given green burials that included the use of biodegradable caskets, baskets or shrouds.

But when a foul odor led investigators to the Penrose location, they found at least 190 improperly stored corpses at the Hallfords’ funeral home in Penrose and Colorado Springs in October last year. They were arrested in November.

“The impact on these family members has been immense,” Mr. Allen said.

He added that the Hallfords deceived grieving families and that “having somebody violate that trust is something that they’ll likely never recover from.”

The Hallfords had also pleaded guilty in federal court last month to conspiracy to commit wire fraud for misusing more than $800,000 in Covid-19 pandemic relief funds from the Small Business Administration, the U.S. Attorney’s Office for the District of Colorado said at the time.

They each could face up to 20 years in federal prison, according to the authorities. The Hallfords are scheduled to be sentenced in March on the federal charges, according to court records.

Instead of using the money they were given by the government or customers to bury or cremate bodies, the couple spent thousands on vacations, jewelry from Tiffany & Company, and items on Amazon, according to court records.

“The Hallfords collected in excess of $130,000 from victims for cremation or burial services, which they never provided,” the federal indictment said.

Lawyers for the Hallfords did not immediately respond to emails seeking comment on Saturday.

The Hallfords gave urns filled with concrete mix to survivors instead of remains of the deceased and provided the wrong bodies for cemetery burial, the indictment said.

Some of the bodies that were found last year at Return to Nature were of people who had died as far back as 2019, the authorities said.

“He laid in the corner of an inoperable fridge, dumped out of his body bag” for four years, David Page, a relative of a person who died in 2019 and whose body was found in one of the funeral home buildings, said outside the courtroom after the guilty pleas, The Associated Press reported.

To conceal the gruesome collection of bodies at the funeral home locations, the couple prevented outsiders from entering their buildings, covered the windows and doors, and lied about the source of the odor, the federal indictment said.

In 2021, Colorado became the second state, after Washington, to legalize human composting that would allow bodies to be turned into soil.

Colorado is the only state that does not require education, certification and licensure for employees in the funeral home industry, according to Colorado state lawmakers.

The case against the Hallfords has prompted a push by state lawmakers to establish a licensing process of funeral professionals in Colorado.