Poor puppy! I'm so glad it is ok!
However, having sadly had more than a few dealings with dog fighting rings in my years of works with shelters, I have to say that honestly doesn't sound like the work of dog fighters.
It seems like a lot of trouble to go to to get one pit puppy ... when they invariably have several females with litters at any given time. And pit puppies are not used as bait dogs ... why would they kill a puppy that might grow up to be of use to them?
I would say that was done by pranksters/vandals who just wanted to break in and cause as much trouble as possible, and happened to see a cute puppy they wanted to steal once they got in there. Once they realized it was all over the news, they ditched it before they could get caught.
"We give dogs the time we can spare, the space we can spare and the love we can spare. And in return, dogs give us their all. It's the best deal man has ever made" - M. Facklam
"We are raised to honor all the wrong explorers and discoverers - thieves planting flags, murderers carrying crosses. Let us at last praise the colonizers of dreams."- P.S. Beagle
"All that is gold does not glitter, Not all those who wander are lost; The old that is strong does not wither, Deep roots are not reached by the frost. From the ashes a fire shall be woken, A light from the shadows shall spring; Renewed shall be blade that was broken, The crownless again shall be king." - J.R.R. Tolkien