I like Journey11's thinking. If necessary, quote the law that allows shooting the dogs, especially since you caught them in the act.
You sound like you researched the statutes about it so you can suggest the dog owner call the sheriff's office if they have any doubt about the legality of you shooting them, as well as the possiblity of their being forced to be responsible for getting them destroyed themselves. That can be pretty darned expensive even if they don't care much for them.
I'd start out trying to be as friendly as possible, or, at least very polite, then, escalate only if that doesn't work.
You sound like you researched the statutes about it so you can suggest the dog owner call the sheriff's office if they have any doubt about the legality of you shooting them, as well as the possiblity of their being forced to be responsible for getting them destroyed themselves. That can be pretty darned expensive even if they don't care much for them.
I'd start out trying to be as friendly as possible, or, at least very polite, then, escalate only if that doesn't work.