Okay, I reread the article . . . It sounds like both dogs were running loose near the highway. When the boxer attacked the first time, the officer tazered it, the dog retreated, then it attacked him again while he was leading the rottweiler to his patrol car. He fired a shot in the air which scared it off, then finished putting the rottie in the car. Then he went back to try to catch the boxer and it attacked him again. He tazered it but it continued attacking until finally he shot it.
Very sad for the dog, but the officer did try to defend himself nonlethally several times, so I don't blame him. They mentioned it was in Kootenai County, perhaps they don't have animal control there like Spokane County does.
I'm not sure where the mother and child fit in, as they're just mentioned in passing in the first line of the article as being the reason the officer was out there. It doesn't sound like the dogs were theirs or that they knew the dogs.