the dogs have to have tickets issued three times against them in order for a court to be allowed to make the decision to put them down.
Do not poison the dogs, you'll only get yourself in HUGE trouble.
What I WOULD suggest, however, is possibly trying to BAIT them. Get something else to happen, get them to attack something/someone else, report it, and voilla - they have their third violation and the dogs will be eliminated.
Jcrim is right, however - the only thing you could win in a suit against them is the monetary value of your dog.
We learned all this in the "law" section of our vet-tech courses. No state will allow for punitive damages to be rewarded in the case of an animal/pet. One case did happen to award a woman punitive damages in the lower courts, but when the defense appealed the case it was promptly overturned. Animals, according to the law, are regarded as possesions. Nothing more.
I am so sorry this had to happen to you and your beautiful dog. No one should ever have to endure this, and I am rooting for you.