I live in a semi-rural part of Texas where we raise chickens and other small livestock on our small-acreage homestead. My main gig is marketing, but I also groom dogs for a little extra income but mostly because I enjoy it. I absolutely love dogs. So much that I specialize in "gentle handling" grooming, which means most of my clients are old, sick, nervous, or aggressive dogs that other groomers won't take, and I usually opt not to restrain them while I'm grooming because it can cause stress and breathing problems. However, despite all of this, I have never been bitten in all my time grooming independently.
I say all of that because I want to make it very clear that I respect that dogs are thinking ,feeling creatures with an innate right to be treated without cruelty on their terms as dogs, not as human-replacements or chattel (even if the law regards them as such). However, I feel the exact same way about all of the animals in my care.
I will not allow a dog to remain in my care or otherwise on my property if they are terrorizing my other charges. My chickens have feelings and thoughts, as well, and they, too, have a right to live without cruelty. When a dog terrorizes or kills a chicken, it is almost always cruel, because the dog did not need to kill that chicken. They almost certainly didn't need to eat that chicken or risk starvation, and most of the time they don't eat what they kill anyway. I can understand a raccoon, a fox, or a hawk killing my chickens. They live on the edge of starvation and have no one to care for them. It is my duty to protect them, not the predator's to change their nature.
It is the same with dogs. The dog is following their nature, and it is the duty of whomever is responsible for that dog to protect them from following that nature into acts of cruelty. If the dog has no owner and is genuinely hungry, I will make an effort to take it in, bring it to health, and rehome it, but this is not always possible. It is also not the usual situation. The vast majority of dogs that end up on my fenced and locked property are there because their owners do not or cannot contain them, and they don't understand -- or don't care about -- the consequences of allowing that dog to roam. Furthermore, it is almost always repeat offenders.
Size and breed is not always a reliable predictor. I have had an entire flock of guinea fowl wiped out by a small dachshund-minpin mix, and I have had massive pit bulls run away from my free ranging rooster. Dog breeds that were created for hunting fowl (spaniels, sight-hounds, etc.) are high risk, but other breeds seem to be entirely down to the personality of the dog. Despite their reputation and their overwhelming numbers out here, pit bulls don't always attack my livestock, but when they do, they maim them horribly due to their bite-and-shake method. I've healed some chickens from dog attacks, but pit bull attacks are invariably deadly, and pit bull owners are invariably in denial about their dog's ability to cause that kind of damage.
Prior behavior with people is also a terrible indicator. I have had two of my own sweetest dogs stalk and kill multiple fowl for sport, leaving scenes of carnage behind that you can't imagine, only to jump up on the couch afterwards and snuggle me in the most loving way possible. I euthanized both of them myself, because it would be irresponsible to keep a dog like that around my livestock, and immoral to adopt it out to the public knowing that it has killed livestock, and that statistics show that dogs who do tend to injure people eventually, too, especially children.
I also have dogs who create scenes so precious that the photos are worthy of TheDodo,com, sleeping in a warm pile of baby chicks and bravely protecting them from predators when the chicks got old enough to live outside. One of these dogs is a complete jerk to other dogs and is a bite risk to people she doesn't know (she's never bitten anyone, yet, but I don't take her out in public for that reason). So, I know that not all dogs kill chickens, and how they act toward people or other dogs is absolutely no indication of how they will act toward prey animals.
But owners are rarely good at judging this. It is the same with my grooming clients. Some of the worst-behaved dogs that threaten to bite the quickest and require the most time and patience to groom, are the ones the owners insist are the sweetest babies who would never hurt a fly. On the contrary, dogs whose owners worry about the most are often the easiest-going and sociable dogs once their owners are gone and not making them feel like there is something to be anxious about. I groom out of my home, and some of my clients can be allowed to run around the house and the yard without a leash and they never bother anybody else. Others have to be watched strictly and kept on a lead at all times. I have never, ever had an owner accurately predict which kind of dog their's will be once they leave.
All of this is to say that although I know most people love their dogs, they don't understand them. They think their dogs are furry human children and this makes them utterly irrational about their dog's potential to be deadly to other animals. These same people often don't think of chickens as anything other than a food item in the grocery store, and they can't process how difficult it is, both financially and emotionally, to lose one to their dog. However, it isn't just chickens. I have seen people try to save dogs who have maimed small children, because the dog "just lacked training" or "needs a proper environment" or something else like that. These people often make petitions like the one the OP has against him.
I wish better education for the public existed about dogs. Most otherwise well-meaning, good-hearted people just have no idea how their dog's brain works, or how important it is to treat a dog with respect for its nature. It's fine to love a dog intensely and cuddle it, dress it up in cute clothes and cook meals for it, as long as you also know that the dog is not a human child. It can never be. Because of that fact, if a dog is allowed to run loose, follows its nature and kills or terrorizes someone else's animals on their property, the cruelty lies not in the person who takes deadly action to protect their animals, but in the dog's owner whose own selfish need to imagine that their predator is a surrogate child resulted in neglect for the proper protections and restrictions a predator requires to live responsibly in a community.
All of that said, I think it is in the OPs best interest to not speak further on this incident here or anywhere else online, now that everyone here knows the specific incident with which he is connected. If his lawyer has not already advised him thus, anything he says here can be used for evidentiary purposes in court.