The scene that confronted Goochland County Sheriff Jim Agnew and his deputies was so grisly that he had to pause as he described it in front of reporters.

“I observed, as well as four other deputy sheriffs observed, the dogs eating the rib cage on the body,” Agnew said at a news conference this week.

The series of events that led to that gruesome scene — two dogs guarding Bethany Lynn Stephens’s bloodied remains after authorities say they mauled her to death while on a walk in rural Virginia — have been the subject of speculation, rumors and anger. Why did these two dogs, which friends said had a strong bond with Stephens, turn on their most important human? Agnew doubted that the question would ever be clearly answered.

But one thing is certain: The attack could have never happened out of the blue.

“I don’t think they were walking in the woods and they eyed each other and said, ‘Now is the time to attack her,’ ” said Liz Stelow, a clinician at the veterinary school at the University of California at Davis.

A stimulus that triggered an aggressive reaction, a sudden change in the dogs’ home life, behavioral changes that they might have been going through as they matured, or a combination of all of these, could have been contributing factors, experts say. For something as terrible as Stephens’s death to happen, there needs to be “a sort of perfect storm of events,” said Marjie Alonso, executive director of the International Association of Animal Behavior Consultants, though what those events were remains a mystery.

Stelow, a certified veterinary behaviorist, said fear is statistically the most common underlying cause of aggression among dogs.

“Now that does not mean we don’t see aggression coming from dogs that are not experiencing fear in that moment, but the overwhelming majority of aggression is part of a fight-or-flight response,” Stelow said. “So you’re in a position where you must do something, and the thing that you find yourself doing is inflicting harm.”

“Almost all of the aggression I deal with clinically is based on fear,” Stelow added. “Everything I’ve read about the case suggests that what likely happened is there was a triggering event, and the dogs either turned on each other and she became involved, or they turned on her because of something that happened, some external stimulus that happened.”

There’s also a concept called predatory drift, said Alonso, a Massachusetts-based certified dog behavior consultant. The term, coined by veterinarian, dog trainer and animal behaviorist Ian Dunbar, is described as “the kicking in of predatory reflexes in an interaction that begins as a social interaction.”

And something has to provoke it, Alonso said.

“Let’s say she was running with them and she fell and she was shouting because she got hurt,” Alonso said. “It’s possible — and I can’t say that this is what happened — that that triggered a response for one of the dogs, maybe, to bite her out of excitation, out of fear, whatever that might be, and caused the other dog to also turn on her.”

Stephens was found dead Thursday evening in a wooded area about a half a mile from a main road. Authorities said the 22-year-old had been gone for about a day since she left to walk her dogs, so her father went out to look for her in the area she frequented. There, he found the male dogs, Tonka and Pacman, near what he first thought was an animal carcass.

Posted by Bethany Stephens on Monday, July 17, 2017

Authorities said the bite marks on Stephens, including the ones on her skull, were consistent with canine marks, some of which were inflicted while she was still alive. They have ruled out other possibilities, such as domestic violence, sexual assault, strangling, stabbing and the involvement of a larger animal, like a bear.

The young woman’s death shook Goochland, Va., a rural community about 30 miles outside of Richmond, and sent a barrage of phone calls, emails and online messages to the sheriff’s department. Agnew, the sheriff, said many were personal attacks against him. Others accused his department of not doing a thorough investigation, believing that there was no way Stephens’s dogs could’ve attacked her. On Monday, Agnew decided to privately show photographs of the scene to local media and publicly reveal the graphic scene he and his deputies witnessed. He said it was an attempt to be transparent without revealing too much.

Agnew said revealing more information has slowed the flurry of angry messages and misinformation, but it has not stopped it.

Some of the anger, at least online, was fueled by a characterization of the dogs’ breed. Agnew said family members described the dogs to authorities as pit bulls — a generic term for dogs with a square, blocky head and an athletic build — though the specific breed is unclear.

“When people say it was a pit bill, it’s kind of an easy go-to,” Alonso said. “There may be pit bull in those dogs, but it doesn’t describe the dogs necessarily. It’s describing what they look like, not what’s in them.”

Alonso said whether a dog has a tendency to be aggressive does not necessarily depend on the breed.

“We tend to label aggression as something that’s inside the animal. That’s not it. Aggression is a circumstance,” she said. “If I corner you in a dark alley and you punch me, are you being aggressive?”

Stelow, the University of California clinician, said that bully breeds, such as an American pit bull terrier and a Staffordshire bull terrier, are statistically highly represented in incidents of fatal dog bites and attacks in the country. But that likely has less to do with their behavior and more with their physical abilities, she said.

“If you look at the body type, they have large powerful jaws and they have large powerful bodies,” Stelow said. “They can overpower someone and inflict great harm.”

Investigators in Goochland County said they’re still working to find out more about the dogs’ lineage and history. Sgt. Mike Blackwood, of the sheriff’s office, said Stephens got both of them as puppies. One of the dogs was owned by someone else before Stephens adopted him.

Investigators also are still uncertain about the dogs’ exact age, but Blackwood estimates they were about 2. That could provide another explanation.

The dogs would’ve been in the middle of maturing, which happens between ages 1½ and 4, said Ilana Reisner, a veterinary behaviorist from Pennsylvania. Aggression toward each other and toward people is more likely as dogs mature.

“They might historically have been very sweet, and aggression to people never or rarely seen, and still have flipped over threshold to arousal and aggression at this age,” Reisner wrote in a Facebook post.

Experts also say that change in environment could affect a dog’s behavior.

At the news conference earlier this week, Blackwood said Stephens had been living elsewhere and had left the dogs with her father. The dogs, which were previously indoor animals, were left in a kennel outside with little human contact, aside from a visit from Stephens about five times a week, he told reporters.

Stelow said she often sees dogs suddenly showing signs of aggression because of changes in their lives, such as a new person moving in or their owner moving out. Even changes in pet owners’ schedule could be stressful.

“So I’m already in another uncomfortable environment where I don’t have the things I’m accustomed to. I have limited contact with my most important human. I don’t understand what is happening, and this is stressful to me,” she said. “Every walk became much more stimulating. . . . Now I’m in a situation where what might have been a tolerable stimulus is now a big trigger because of all the other stressors I’ve been experiencing.”

The dogs were euthanized Saturday and are being preserved. Agnew said his department has found a lab that will perform a necropsy and extract anything that may be needed for further analysis.

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