On Easter Sunday my wife and I were at the green area near the tennis courts and swimming pool off 105th st. There were several dogs there including a white Bull Terrier female named Gracie. Gracie was off leash and not responding at all to verbal commands from the man who was there with her. After we saw him put her on a leash, we started playing ball with our Border Collie Marco. Marco is obedience and agility trained and is very responsive to verbal commands. After a few minutes Gracie came bolting off, again off leash, and viciously attached Marco. My wife tried to intervene and received a nasty bite to her hand. I did not get the man's name but as he hurried away, I demanded his phone number which he finally provided. It turns out to be a non-working number. We need any information to identify this person as he will need to provide proof of current registration and vaccinations for Gracie. If anyone has information that will help locate the owner, please contact us at ngehr1@cox.net. Thank you for your help.