The police force who deliberately ran over a dog running loose on a motorway is now under investigation by the Independent Police Complaints Commission (IPCC).
North Wales Police referred itself to the IPCC after thousands of people complained about its officers running over the foxhound on the A55, near Llandudno, on Monday.
The force claimed the dog was "dangerously out of control" on the dual carriageway, but animal protection groups have said that the incident shows that officers "desperately need a crash course in humane animal control".
North Wales Police said that efforts had been made to catch the dog, before officers decided to destroy by running him over.
The same force previously Tasered a sheep on the same road after it disrupted traffic. The ram was incapacitated and survived, but the RSCPA investigated.
The killing of the dog has drawn widespread criticism but was backed by its owner, police said, who was "devastated" but understood the decision.
Chief Superintendent Sacha Hatchett said: "He said he appreciates that given the risk to human life, the officers made the correct decision. He is supportive of the police as had there been a serious accident, he said he could not have lived with himself."
But there were accusations of "animal cruelty" and calls for the officers involved to face criminal charges among the 15,000 comments on the force's Facebook page.
Vet Marc Abraham said he was "horrified, disgusted and upset" at the animal's treatment.
He told Sky News on Wednesday: "I think the general public demand an explanation. Surely at three am in North Wales they could have shut the road. What if it had been a mentally ill person, would they have done the same?”
"If they’ve closed the road, that would have mitigated the risk.
"If you’re driving at that speed in your vehicle you’re causing another risk. It doesn’t make sense at all."
The RSPCA called it a "tragic incident" and said it would be contacting North Wales Police, while animal rights charity People for the Ethical Treatment of Animals (Peta) condemned the killing.
Peta director Mimi Bekhechi said: "This could just as easily have been a frightened human being or someone with a mental illness. These officers desperately need a crash course in humane animal control if they believe that crushing a dog under a vehicle was the best or only available option."
Hatchett defended the officers, saying it was "a difficult decision", with their "overriding concern being the safety of road users".
She said: "It was a fast-moving incident, officers at the scene were in contact with the force control room and other options were considered. Officers used their vehicle to partially close the road, the use of firearms was also considered, but ruled out due to public safety.
"Regrettably the urgency of the situation meant that the decision was made by the officers at the scene to take the action that they did."
She added: "At times we are called upon to destroy animals in the course of our police duties, and such decisions are never taken lightly. This decision was not taken lightly.
"In North Wales we have had people lose their lives in collisions caused by animals running loose on the road. We understand that people are upset that a dog was killed, the officers are also upset, it is regrettable, but we will never know what could have happened had such action not been taken.
"The force has voluntarily referred the incident to the Independent Police Complaints Commission because of the level of public concern. It is also being reviewed by the force to ensure we examine options available to officers and we will liaise with RSPCA Wales and others in doing this."
North Wales Police and Crime Commissioner Winston Roddick said it was a "difficult judgment to make" and said he would be raising the incident with the force.