Here's why these kind of stories happen and why pits get a bad rap. First, go to any shelter across America and you will find that 90% of the dogs are pit bulls. Then ask on top of the adoptable pit bulls they have, how many are euthanized on a weekly basis.
The problem with pits isn't that they're bad dogs, they're actually great. The problem is douche bag owners who think they can breed them and make a profit. What happens is you get "backyard" breeding and you get bad temperaments and bad genes. This cycle is endless. Then, some of these dogs that have no pedigree and were bred improperly end up in homes and these incidents occur.
I've previously owned 2 pit bulls and they were sweet dogs. Awesome with kids. They are very very strong and anyone who owns them also needs to know HOW to own them and be responsible. About 10 years ago I did dog training professionally and we used to have classes for reactive(aggressive) dogs. Occasionally you would see pit bulls in the class, but more often than not, you had every different breed you can think of. Many of these dogs came from horrible back grounds like puppy mills and abusive owners. Some went to classes multiple times and had tons and tons of training and still would attack their owners or other people. Sadly some were put down. In my experience as a trainer, 99.9% of a dog's aggressive nature steamed from idiotic owners. People get a dog based on how it looks, they do no research into the breed and what being a responsible owner of a particular breed means.