Would a rooster pick a "favorite" hen and kill the others in a small flock?

I have had terrible luck with my chickens the last 2 summers. This past summer, I lost 34 chickens. To my dogs. In 2 different batches. Both times it happened right as they were old enough to lay. Didn't know for sure which dog, so didn't get rid of any of them. Should have gotten rid of all of them. Anyway. Today's question:

2 weeks ago I had 6 surviving chickens. 2 roosters, 4 hens. Last week, I noticed my best layer (and oldest hen) staying out of the chicken house at night. Wouldn't roost. The night it was to get below freezing, I made her go in. The next morning she was all beat up on her head, and bald and blind on one side. So I isolated her. The next morning, when my son went for eggs, he found a dead hen in the corner of the chicken house with no head. Griped me, but I thought how weird. Maybe he didn't latch the coop. That night I made sure I closed the coop. Next morning, another dead chicken with no head. This time I caught one of my dogs in the chicken yard, so I got rid of her. Problem solved. Nope. The next morning, same thing. Dead hen in the corner of the coop, with her head hanging by a tendon. This whole time, the surviving chickens have been roosting up in the rafters of the house. Couldn't figure it out, so I started looking around and realized that the brood box lid was propped up against the outside back wall of the coop. We don't have chicken wire on the eaves, cause I thought a predator would have to be Houdini to get in there. Anyway, I moved the lid and waited. No more dead chickens. Course I'm down to 3 now, including the wounded one. This morning she looked better, so I fixed her up a protected run area so she could go back to the chicken yard when she wanted to. I hadn't been in the house 15 minutes when I saw my female dog take off and heard the hen squawking. I thought my cat maybe was chasing her. When I got to the chicken yard, the rooster was on her. He followed me around and jumped at her the whole time I was moving her. I had to beat him off with a stick. But as soon as I got her out of his sight, he went back to his normally quiet, scardey-cat self.

WHY WHY WHY? And is it possible that HE killed those 3 chickens because he only wanted his favorite? And now, what do I do with the hen? She's a good hen. Very docile, good layer, about 18 months old. If she rebounds from this second attack, she'll be blind in one eye, but she's a good layer. He seems to have no trouble with the Barred Rock hen that's left, so should I just wait until spring and see what happens when I introduce the new batch of chickens to the yard? Or sell him and start over? He's a beautiful bird, and I like the crowing (we live in the woods).

Thanks for any comments!