We were just having a discussion about this yesterday. This seems to be getting more and more common. In the search for the next "thrill" I think alot of gangsta wannabee's are getting these attack dogs, and frankly, they can't handle them. The things need to be banned.
I'm not sure a complete ban is appropriate, but requiring a BIG liability insurance policy is. That would effectively illegalize ownership by the unstable, chronically unemployed lowlifes who currently own nearly all of the vicious dogs (pit bulls and other breeds). Even the ones who have a bundle of money from dealing drugs still wouldn't be able to get a policy, because insurers would have a lot of other requirements, like securely fenced yard, no criminal history, no history of pet-related law violations, etc.