I recently talked with a lady who had been an animal control officer and had run no kill shelters. We discussed the pit bull and she told that a specialized breeding program was done in Cuba during the Batista time. The pits were crossed with another breed whose name I can not remember and the result was a pit that would track down and kill escaped prisoners. She said it was cheaper than a bullet. She told me that if you track the lineage of any pit involved in a human attack you will find that Cuban strain somewhere.
I helped train dogs years ago and have had limited contact with pits but the ones I met well mannered and never a problem. I read somewhere that in England they were known as the Nanny Dog, owners would tie them to the baby stroller and leave for a walk thru the park knowing their child was safe.
A whole helluva lot different in temperament than any pit bull I've ever been around or seen. The pit-bulls-as-nanny-dogs myth is a sad and malevolent fantasy, debunked not just by common sense and understanding of breeding, but by stubborn facts right here.