I have a suggestion....
Call a Pit Bull rescue organization near you and tell them about the dog. Tell them it's a nice dog, but runs free all the time and you think it's being mistreated.
I can almost guarantee that someone will swoop up the dog and find a new home for it.
I've dealt with dog rescue organizations before. The people involved can be very aggressive about getting the dog off the street and into a home where it will be taken care of.