well after you shot it how did you fine out it was his dog?
if it was in your chicken pen killing your birds did you have your gun in your hand when you first saw it, or did you see the terrier then run in doors find your gun cabinet keys get your gun out then run outside while loading your gun then aim and fire, in all that time would it have been more easy to catch the dog up?
you also say that the dog was dangrous how did you know this or was it hear say ?
also you say why does the keeper have a dog that kills ? may be its a hunting dog ?
i just hope your dog never gets out