The remains of over 100 dogs were found at a Northern California animal sanctuary during an investigation into suspected animal cruelty, the Humboldt County Sheriff's Office said on Friday.

The investigation into Miranda's Rescue in Fortuna began April 22 after the sheriff's office said they received credible information of allegations of felony animal abuse, animal cruelty, fraud and conspiracy. A search warrant served May 1 at the site resulted in detectives finding evidence related to the investigation, the sheriff's office said.

Investigators then returned June 23 with a second search warrant to dig at the 50-acre property and search through the buildings. The sheriff's office completed the search on Friday and announced they had unearthed the intact remains of 117 dogs from two separate dig sites.

The skulls of 21 dogs, hundreds of bones and six loose microchips were also found near the dig sites.

"Seventy of the dogs were X-rayed on site, and many of those animals showed evidence of bullet fragments," the sheriff's office said.

The rescue describes itself as a "no-kill rescue," and in a statement by founder Shannon Miranda posted to their website, she says, in part, "Shelters often turn to rescues like Miranda's Rescue as a last resort for these harder-to-place animals. We accept animals from shelters throughout Northern California and provide shelter services to local communities without their own facilities. Miranda's Rescue is a no-kill rescue. We do not euthanize animals simply to make space. However, as we state on our website, there are rare circumstances in which euthanasia may be necessary."

In a separate statement posted June 18, the rescue denied operating as a money-making scheme and said euthanasia was performed only in rare circumstances involving terminally ill animals or those posing a serious danger to people or other animals. CBS News Bay Area reached out to Miranda's Rescue for additional comment but had not received a response.

The sheriff's office said forensic veterinarians and the USDA examined 70 of the dogs and preliminarily determined the cause of death for many of them to be gunshot wounds. The intact remains were taken as evidence, and the sheriff's office said most of them were microchipped and work is being done to identify those dogs.

Remains of dogs too decomposed to be recovered were also found in the same field, the sheriff's office said.      

During the search, investigators found a location inside a barn where they believe the dogs were killed, and according to the sheriff's office, 600 dog collars were found in the same area.

"There is a tremendous amount of data to process, witnesses to interview, and evidence to examine. The Major Crimes Division is laser-focused on this case and will continue working with our state and federal partners to examine every lead," Sheriff William Honsal said.

Honsal said Miranda's Rescue accepted animals from shelters throughout California, charging fees ranging from hundreds to several thousand dollars per animal.

Investigators also revealed the scope of the case may extend well beyond the remains already recovered. According to Honsal, more than 900 animals were transferred to Miranda's Rescue from shelters across California over the past five and a half years.

"So far, we were able to account for only 100 or so that have been adopted," Honsal said. "We have 730 animals that are unaccounted for."

No charges have been filed, and the sheriff's office said once they complete their investigation, if they believe there is sufficient evidence to support the allegations, the case will be forwarded to the district attorney for review and consideration.

"The Humboldt County Sheriff's Office would like to inform the public that, due to the nature and complexity of this investigation, the evidence review process will require a significant amount of time," the sheriff's office said.

A news conference will be held on Monday at 2 p.m. by the sheriff's office to provide more information.

The discovery has stunned animal rescuers across California, including Bay Area organizations that previously entrusted dogs to Miranda's Rescue.

Meanwhile, Bay Area rescue operator Dan Martinez said people across California continue searching for answers about pets they surrendered to Miranda's Rescue, with many reaching out through social media hoping to learn what happened to their dogs.

Martinez said there has been one bright spot amid the investigation. A dog named Oliver, which he removed from Miranda's Rescue several weeks ago and brought back to the Bay Area, has since been adopted into a new home and renamed Miles.