You suggested that the dog story got prominence in the news report because it was rare.
Actually, the story of what this creep did to the little girls had been in the news for some time. It was already well-known, and there was appropriate outrage. Then he molested the dog and got caught, so the story about the dog is just an update that is getting national attention.
It's not like the dog is more important than the girls. What he did to the dog is just another nail in his coffin.
The first time it has happened?
You can't be serious......bestiality is pretty rare, but not that rare. I am sure hundreds of dogs have been raped over the centuries since Europeans settled in America.
If a horny pervert will do goats, horses etc....they sure as heck would do a dog.
Don't underestimate the perversity of the sinful human mind.
However, you are right about uniqueness. That is a news value..when something is odd or rare, it gets covered.
Also, since this occurred a year after the rape of the girls and is the latest incident, obviously this would get the attention.