We had a similar thing happen to us last year, we managed to get the number off the ring, rang the pigeon ganciers club up and they put us in touch with the owner, who came to pick it up and off he went, I rang him a few days later to ask how the bird was, and he told me he had rung its neck as it was a racing pigeon and no good to him if it could not race.
We have again had a similar situation and the owner did not want it back as he lived over 100 miles away so we found the following website, and posted info on it, and we had so much help from people who love all birds, that someone came to collect the bird, this bird is now living in a sanctuary as it will never fly again, it has a partner now and is obviously happy.
Website is; www.pigeon-life.net
Just click on member exchange, chat forum, they are a great bunch of people, very friendly.
Hope this has helped.