CANON CITY, COLO. -- The awful smell seeped from a neglected building in a small Colorado town for days, followed by a report that made police take a closer look at the "green" funeral operator's storage facility. Inside, they made a gruesome discovery: At least 115 decaying bodies.

Investigators were tight-lipped Friday about exactly what they found inside the Return to Nature Funeral Home in Penrose, Colorado, but their plans to bring in teams that usually deal with airline crashes, coroners from nearby jurisdictions and the FBI pointed to a grim mess.

A state document, meanwhile, alleged funeral home owner Jon Hallford tried to conceal the improper storage of corpses. He claimed he was doing taxidermy at the facility, according to the state suspension letter dated Thursday.

Hallford acknowledged that he had a "problem" at the property, the Colorado Office of Funeral Home and Crematory Registration letter said. The document did not elaborate on the taxidermy and alleged improper storage of remains, but the facility's registration has been expired since November.

No one had been arrested or charged. Text messages to the funeral home seeking comment went unanswered. No one at the business picked up the phone and there was no working voicemail.

Funeral home officials were co-operating as investigators sought to determine any criminal wrongdoing, Fremont County Sheriff Allen Cooper said at a news conference where he called the scene inside the building "horrific."

On Friday, a sour, rotten stench still came from the back of the building, where windows were broken. Coroner's officials from Fremont County and nearby El Paso County parked their trucks outside and discussed among themselves as they walked around the building.

Some identifications would require taking fingerprints, finding medical or dental records, and DNA testing in a process that could take several months, Fremont County Coroner Randy Keller said. Families would be notified as soon as possible after body identification, he added.

Family members who have used the funeral home were asked to contact investigators.

As the news broke, Mary Simons, 47, couldn't help but wonder if her husband was inside the building. Darrell Simons had lung cancer and died of pneumonia in August, a few months shy of their 13th anniversary. Mary Simons hired Return to Nature Funeral Home to cremate him, but the ashes never arrived.

Sitting in the rocking chairs that Simons and her husband spent long hours in at their home in nearby Florence, Colorado, she remembered him proposing to her by running, sliding on his knees and popping open a box with a rock inside, and the small pond he built with a trickle of water to calm her anxiety. She'd finally begun to turn the corner of grieving, she said.

"Suddenly it's like `oh my God', I've lost him all over again," Simons said through tears. "It's like the grieving process is starting all over again."

Police told Simons the process of finding out whether her husband's body was in the building would be slow, she said.

The FBI was bringing in teams with additional training and specialized equipment that process "scenes of national magnitude," such as major airline disasters, Denver-based FBI Special Agent in Charge Mark Michalek said.

The bodies were inside a 2,500-square-foot (230-square-metre) building with the appearance and dimensions of a standard one-story home. The funeral performed burials without embalming chemicals or metal caskets, using biodegradable caskets, shrouds or "nothing at all," according to its website.

The company charged $1,895 for a "natural burial," not counting a casket or cemetery space, and until July offered cremations, too.

Under Colorado law, green burials are legal but state code requires that any body not buried within 24 hours must be properly refrigerated.

Deputies were called in Tuesday night in reference to a suspicious incident officials haven't yet described. Fremont County Sheriff's Office investigators returned the next day with a search warrant and found the remains.

Joyce Pavetti, 73, could see the funeral home from the stoop of her house and said she caught whiffs of a putrid smell in the last few weeks.

"We just assumed it was a dead animal," she said.

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Associated Press writers Amy Beth Hanson in Helena, Montana, Mead Gruver in Cheyenne, Wyoming, Matthew Brown in Billings, Montana, and news researcher Jennifer Farrar in New York contributed.