"But, they had a legal right to be there. And, the shooting only began when the officers were attacked by pit bull."
He they done their job they would have know there was a dog there and that also would have militated against sending in plain clothes officers with their guns blazing.
They did their job. They turned sirens and flashers before they approached. They legally entered the house. And, shooting only started when the couple's friendly pit bull attacked one of the officers. The officer killed the pit bull in self-defense.
The officers did nothing legally wrong nor did they violate any procedures. If you have problem with that, demand the law be changed and see if there is enough support for it to be changed.