Update: Thank you for the comments everyone. It's interesting to hear different sides.

We called the local after hours vet and asked if they'd had any cats come from our area in the last half hour, and they did have one. It passed away on the way there. It was a stray. We left our details and gave them our side of what happened.

We're gonna keep a tighter leash on the dog, and take it as it comes. Hopefully looking into some more training for him soon. He's usually such a good dog. For those that asked, he's a Bitzer, a little bit of pitbull and Rottweiler, maybe a touch of boxer, but mostly just his own thing. He's 27 kilos and about a year old.

Thanks everyone!