LOS ANGELES — Linda Bruno called her Pennsylvania cat rescue the land of milk and tuna. It thrived for years as people sent pets they couldn't care for from hundreds of kilometres away -- unaware it was a death camp for cats.

Investigators who raided the place two years ago found killing rooms, mass graves so thick they couldn't take a step without walking on cat bones and a stunning statistic: Bruno had taken in over 7,000 cats in the previous 14 months but only found homes for 23.

In doing so, she had become a statistic herself, one of an increasing number of self-proclaimed rescuers who have become animal hoarders running legal and often non-profit charities.

Rescues and shelters now make up a quarter of the estimated 6,000 new hoarding cases reported in the U.S. each year, said Dr. Randall Lockwood, ASPCA's senior vice-president of forensic sciences and anti-cruelty projects.

"When I first started looking into this 20 years ago, fewer than five per cent would have fit that description," Lockwood said.

Hoarding itself is not a crime in most states, but cruelty is and both can start around the same time -- when one more animal becomes one too many. Rescuers take in rejected, abandoned, abused or stray pets. Some come from municipal shelters as they are about to be euthanized.

It remains a mystery how someone goes from trying to rescue animals to stockpiling them in inhumane conditions without food, water or basic care. No single trigger has been found, but dementia, addiction, attachment disorder, obsessive-compulsive disorder and other psychological problems are often blamed.

"The root of it is really nothing to do with animals. It's to do with people's heads and how they work," said Gregory Castle, co-founder and chief executive officer of Best Friends Animal Society in Kanab, Utah.

The focus on hoarding of all kinds has intensified in recent years due to widely publicized cases and television shows about it. The Hoarding of Animals Research Consortium at Tufts University is urging the American Psychiatric Association to include animal hoarding in its next update to its diagnostic bible.

Some hoarders develop a "messiah complex," seeing themselves as saviours even as animals die. One hoarder told Lockwood: "I wouldn't give one of my dogs to Jesus Christ if he came in the door."

Bruno was seen as a cat saint of sorts and she surrounded herself with volunteers who enabled her and rallied around her when the Tiger Ranch Cat Sanctuary in Tarentum, Pa., was shut down. Some 700 people signed a petition seeking dismissal of the case.

Cats were found in nearly every filthy, stinky building on the 11.6-hectare property. Many were too sick, starved or weak to get to the little food or water available.

The Pennsylvania Society for the Prevention of Cruelty to Animals recovered 391 live cats and 106 dead ones. Thousands were believed to be dead and buried.

Bruno, 47, was sentenced to two years of house arrest and 27 years probation. She was ordered to pay $200,000 in restitution and $21 a day in electronic monitoring fees.

Several agencies received reports of hoarding at Bruno's ranch, but it took months to document. Typically, the accused offer myriad excuses. They claim they are victims of religious and political persecution or contend people are lying or planting evidence.

It's hard to believe the excuses after seeing centimetres-thick feces, urine-stained walls, cages stacked high with starving animals, dead and rotting carcasses, trash, fleas, maggots and diseases, said John Welsh, spokesman for the Riverside Department of Animal Services.

A whistleblower tipped off Welsh's department in 2007 that a nurse, Sylvia Gyimesi, was euthanizing sick animals with a homemade cocktail of vodka and sleeping pills at the Best Buddies Rescue she ran out of her Aguanga home.

In a pair of mobile homes on Gyimesi's property, investigators found close to 150 chihuahuas, dachshunds and poodle mixes, along with some large-breed dogs. Welsh said the stench and squalor were so bad that he had to leave almost immediately. They found graves in the backyard and a paw coming up from the sand near a barbecue.

Gyimesi said a disgruntled helper had snitched on her after being scolded for not working. She denied being a hoarder and said she never euthanized any animals.

"I think hoarders use rescues as an excuse, a facade, a front and they don't recognize it themselves. Their animals are not getting care and they don't want to let any animal get adopted," she told The Associated Press. "I know I had too many dogs and it wasn't the cleanest, but I'm not a frigging murderer."

She turned all but 10 of her animals over to the county and pleaded guilty to a single misdemeanour count of animal cruelty in exchange for five similar counts being dismissed. She had to perform community service and has vowed to never run a rescue again. She has since passed all inspections at her home.

The recidivism rate among hoarders is usually 100 per cent, so Gyimesi is an exception, Welsh said.

Gyimesi said it took her 18 months to rebuild her life after spending a day in jail and cashing out a retirement fund to pay $14,000 in fines and fees.

Fallout from massive hoarding cases has a much broader impact. In summer 2007, nearly 800 cats were seized at For the Love of Cats and Kittens (FLOCK) in Pahrump, Nev.

Vets and volunteers from Best Friends Animal Society cared for the animals, turning the compound into a temporary triage for the starving, disease-ridden cats who struggled to breathe in the 46 C desert heat.

Casinos held adoption events, finding homes for 72 cats. But of the 570 cats at the Best Friends 1,560-hectare sanctuary today, more than a quarter are from the Nevada rescue still waiting to be adopted more than three years later.