One dog has been destroyed and another returned to its owner after the animals were caught following an attack on sheep at Kai Iwi.
Wanganui District Council spokeswoman Sue Dudman said an animal-control officer put down one of the impounded dogs after the owner did not pay pound fees.
She said the other was returned to its owner after being impounded.
"The investigation found that there was no proof this dog was involved."
Nineteen ewes and lambs were killed in the January 7 attack. Others were injured.
Ms Dudman said there was no conclusive proof that either dog attacked the sheep.
"In the case of the first dog, a rottweiler, it was impounded and its faeces were checked over a number of days for signs of blood and wool.
"No evidence was found. This dog has since been registered and microchipped and is now back with its owner. It is securely contained ... "
She said the second dog was seen on the Kai Iwi property but there was no proof it had attacked the sheep. The owner was told the dog was in the pound but did not claim it.