Authorities have unearthed the remains of at least 117 dogs on the grounds of a California “no-kill“ animal shelter, many of them with gunshot wounds.

The Humboldt County Sheriff’s Office confirmed on Friday that it also discovered 21 canine skulls, hundreds of bones and other remains during searches at Miranda’s Rescue Animal Sanctuary, a 50-acre (20-hectare) facility in Fortuna, California.

Investigators searching the site on Thursday located an area in a barn where they believe dogs were likely killed, the sheriff’s office added.

More than 600 dog collars were found nearby, in what Sheriff William Honsal called a “horrific scene.” No charges have been filed.

The shelter’s founder, Shannon Miranda, was approached for a comment.

In a statement posted to the shelter’s website on 18 June, Miranda said that recent media coverage and online commentary “have presented an incomplete and, in some cases, inaccurate picture of our work”.

“At Miranda’s Rescue, our mission is to save as many animals as we safely can—always balancing compassion for animals with our responsibility to protect families, children, other pets, and the public”, Miranda wrote.

The sheriff’s office said it started investigating the shelter after receiving “credible information” in April “regarding allegations of felony animal abuse, animal cruelty, fraud, and conspiracy.”

Miranda’s Rescue collects fees from shelter transfers, as well as donations that it says helps cover the costs of food, housing, veterinary care, medications, facility expenses and staffing.

An affidavit from an earlier search of the property said that the sheriff’s office was tipped off by a pair of animal advocates, one of whom owns property adjoining the shelter and used trail cameras to monitor activity near an alleged burial site.

The advocates later went onto shelter property and dug up dog remains, the affidavit said.

“This investigation is just getting started,” Honsal said in a statement. “There is a tremendous amount of data to process, witnesses to interview, and evidence to examine.”

Investigators using ground-penetrating radar found 117 intact remains in various stages of decomposition buried in an open field, the sheriff’s office said.

They X-rayed 70 of the remains on site and found evidence of bullet fragments in many of them. The cause of death for many of those animals appeared to be gunshot wounds, the sheriff’s office said.

Investigators also found additional remains in advanced stages of decomposition, the sheriff’s office said.

The sheriff’s office said hundreds of dogs were transferred or turned over to Miranda’s Rescue by private citizens and animal shelters.

In his statement, Miranda said, “Miranda’s Rescue is a no-kill rescue. We do not euthanize animals simply to make space.”

However, Miranda wrote, ”there are rare circumstances in which euthanasia may be necessary — when an animal is suffering from a terminal condition or when it poses a serious, ongoing danger to people or other animals.”

“In those situations, we make the most humane and responsible decision we can, always with public safety and animal welfare in mind.”