Sheriff Joe Arpaio, who's made public-relations hay over the years with his animal-protection antics, told reporters that the video proves the shooting was "justified."
The dog was "in the wrong place at the wrong time," Arpaio said, adding that he should have been contained.
In the video, two officers approach Debbie Holm's Mesa home and inquire about the whereabouts of her son, saying they have an arrest warrant for him.
As she explains that she is not in contact with him, her dog, a pitbull named Blue, starts barking loudly from behind a screen door.
"Let me shut this," she says.
When she opens the screen door, Blue runs out of the house at full speed, wagging his tail furiously. One officer jumps in the back of a truck and another shoots him.
When she opens the screen door, Blue runs out of the house at full speed, wagging his tail furiously.
Holm wails: "No! Don't shoot him! You shot him?"
"Yeah," the officer says. "He was going to attack my partner."
Or was he just being friendly? It was a split-second decision by the deputy.
As Blue circles back to the house, the officer in the truck climbs out and asks his partner if he's OK.
"Yeah, I'm good. I'm shaking," the officer replies. "He was right there."
The first officers assures him: "That dog was barreling straight for you. I had my gun out, too."