My cat was killed by a dog last night what can I do about it?

Last night my neighbour turned up at 10o'clock with my beloved cat Ozzy wrapped in a towel. He'd been exploring up the road and entered someones back garden and their dog broke his back and killed him after Ozzy squared up to him. Now I can't rehome another cat because the Celia Hammond Trust who rehome cats in my area, are concerned about this dog having killed a cat once, it may do it again. And rightly so. Now my question is, how can I go about talking to the people who own the dog who did this? I don't want to go all guns blazing in there cos that would really do the situation no good, but I don't even know what breed of dog it is and I would like to ask without them going on the defensive. How can I do this and be as diplomatic as possible, after all, their dog killed my cat - even though he was in their garden, the fact of the matter is, my cat is now dead and buried. He was only 2 years old and beautiful.