One of my neighbours has a dog that is frequently escaping from the garden, both into other gardens and the street, at which point it buggers off. Then, this morning, she has been 'boasting' about it killing a sheep at the weekend. 
She reckons she has rang the police apparently, and they have just told her to keep it on a lead in future. 
I'm wary of reporting as I am not sure what this would bode for the dog's future (it's a staff cross) but it's likely to end up getting run over or shot at this rate anyway and that poor farmer/sheep. 