Napier City Council says it had reluctantly released from a pound a potentially dangerous dog that went on to attack and kill another dog.
The two-year-old pitbull was caught by animal control officers in February and was scheduled to be put down.
But a Facebook campaign raised the $530 in fees the owner needed to get the dog back.
Napier City Council spokesperson Robyn McLean said the attack happened on Thursday, several days after the dog was returned to its owner.
She said the pitbull was chained at another address where a shar pei dog was also tied up, when it broke free and fatally mauled the other dog.
"The Napier animal control officers had warned the family that the dog was a dangerous breed and needed to be well restrained. The outcome could have been a lot worse, especially with children in the vicinity."
Robyn McLean says the council is considering prosecuting the pitbull's owner because of the incident.
SPCA Auckland executive director Bob Kerridge said if council staff thought the pitbull was dangerous, it should not have been released.
He said local authorities have powers under the Dog Control Act to make special provisions for dogs that show aggressive tendencies. Ms McLean was not able to say if the dog had been aggressive when it had been in the pound.