To the OP, you should sue the offending dog's owner for damages to you, your dogs, & your family, & report him to the proper authorities. If this dog is as awful as you say he is, he should be put down before he does this again. If it came onto my property & attacked my tied up dogs, he would've met with my sidearm.
Sound familiar?
I have 2 APBT type dogs, & my (always leashed) dogs are "assaulted" by off leash dogs owned by ignorant inconsiderate asshats all the time. I will not hesitate to protect my 2 pit bulls from the stupid labrador retreiver that comes running over to them (no owner in sight) & starts humping my female, & proceeds to somehown manage to bite me in the ensuing scuffle. This very thing happened to me last month.
The owners are the problem. My 2 dogs (much like my guns) will NEVER attack someone on their own, because I'm responsible for them, & I prevent situations where they may get into trouble. Same as with my protection trained German Shepherd a few years ago.
Dogs are dogs. Pitbulls are the "Strongman" of the dog world. They're strong as an ox, & have endless energy. They are also extremely intelligent. They get the bad rep because of bad owners, not because they're bad as a whole. Statistically, they don't bite nearly as much as other "acceptable" breeds of dogs. I'm not a drug dealer or in another nefarious occupation, although my female pit does go to work with me & meets lots of people during the course of our work day.
Also, no, I'm not negative repping you just b/c you're ignorant in this matter...you have the right to your opinion. You just happen to be wrong on this one, & I say this with the utmost respect.