A Mansfield family is mourning the death of their five-year-old Great Dane after an off-duty officer fatally shot the dog as children played nearby.

"I want to see some justice. I want him to have some accountability," said the dog's owner, Carol Evans.

The off-duty police officer was walking his own dog Sunday evening in the 4200 block of Iron Drive when, according to Mansfield police, the officer says the dog, Caesar, "came at him aggressively."

The officer says he tried yelling at the dog but then felt forced to shoot, using his personal weapon.

"He did go over there, and they kind of started barking, so I said, 'Caesar!'" Evans recalled. "I walked over there to get him. I was probably two to three feet away from him, went to pull Caesar, and he pulled a gun out and shot it."

Two children from Evans's family were riding bikes nearby, along with two others from another house in the neighborhood.

"When I saw the gun in his hand, I panicked, because the kids were right there, and I was like, 'Get the kids inside, get the kids inside!'" Evans said.

"I want to know why in the world would he shot off a loaded firearm literally 10 feet from children," said Evans's husband, Jeff Wempa.

"There was no rustle or tussle of dogs. There was no barking, screaming or anything like that. It was five, maybe eight, seconds," said the family's neighbor, Garrett Martinez.

Caesar died on the way to the veterinarian's office.

"I'm going to be forever haunted," said daughter Jessica Evans. "My best friend died in my back seat, for no reason. He didn't do anything to deserve to die."

The officer's name is being withheld.

His actions are under investigation by the Tarrant County Sheriff's Department.

"The department is continuing to look into this matter as we would with any citizen involved in a similar circumstance," the sheriff's department said in a written statement Monday.