My dog killed our chicken

A few months ago, a little chick got abandoned by its mom so we decided to take him in. We also have a dog but he stays outside in this open area that we built where he runs around freely. Our chicken was almost an adult and for some reason my dad thought it would be a good idea to let the chicken stay with our dog, even though I said not to because our dog doesn’t have any previous exposure to chickens. My dad didn’t listen and did it any way. I would check up on the chicken every hour to make sure he was okay. My dog wouldn’t bother the chicken, he would just sniff it and then walk away. We also have a lot of stray cats around our house, so I was always paranoid that the cat would attack the chicken. I came home from grocery shopping and I went to check on the chicken and he was laying on his side and my dog was standing over him, but he was sniffing the chicken. I don’t know if my dog attacked the chicken or if my chicken was killed by a cat. I went to get my dad and he flipped out on my dog and tried to hurt him. I got mad at my dad for that and I said that our dog didn’t know any better and that it was his fault for putting the chicken there. My dad hates our dog now. I’m upset but I know that my dog didn’t know better, especially since he had no exposure to chickens prior to meeting our chicken.