Growl, Snap.
You get a dog with good muscles and strong teeth, you train it up to be a killer-winner pit dog that wins every fight it's ever in and loves every second of it. Gets to be too good, the mere scent of blood throwing it into joyful rage until there's nothing left alive.
You take something like that out of the pits, put it in normal everyday life, does anyone really, honestly expect it to be a normal pet ever again?
It'll do anything to keep off the chain or away from the bullet, but can it truly be blamed for what happens next time it scents blood?