it's not an evil animal, and not a wild animal:
A dog has a food drive, a play drive, a prey drive and defensive drive, for purposes of my explanation.
The APBT issue is a breeding enhanced behavioral issue - the APBT has the same prey drive as many other dogs, with a few key exceptions. It's prey drive is mainly triggered by other animals, but sometimes, unfamiliar people.
The APBT's prey drive is like a skipping record. It has no final conclusion, and instead, the prey drive blends with play drive. When it is preying on an object, it also is at play, and may be seen wagging it's tail during the attack - like a lab retreiving a tennis ball. It can continue this prey/play for a long time, and you will have many bites because like a cat, the APBT's attack has turned into a game.
Additionally, on the attacks on humans, I think in certain individual animals, there is a heightened defensive drive, which triggers a prey response, and you see the "Play" attack which results in massive damage. To the APBT, what may have started as defense of owner or property, or as prey drive turns into a fun game.
Just the thoughts of a guy who knows a little - - about dogs.
*A little about me: I have owned three APBTs. I have owned many other dogs. I am a hobbiest trainer, and I don't claim anyspecial skill or ability because of that - a hobbiest is NOT a pro, and I of course defer to the pros. I have also shown Great Danes, which is a completely different topic than the behavior of the APBT, but I throw that in for what its worth.