Photos from a police investigation into the deaths of more than 200 sheep on a north Otago farm.

This article contains content that some readers may find disturbing.

When death came to Ngapara, it came savagely and without warning.

Dozens of bloodied sheep, many with shattered skulls, were found piled at the bottom of a limestone rock at a North Otago farm.

NZ POLICE/SUPPLIED Police officers at the scene of a sheep massacre on a Ngapara farm, near Oamaru in 2014.

And Peter Stackhouse blamed himself.

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* Ngapara community at odds with police over sheep deaths

* Sheep massacre appals farmer

* More sheep killed

"I thought I had poisoned them all somehow ... then I saw the holes in their heads," the farmer said.

Nicola Wolfe The Ngapara community remains convinced more than 200 sheep killed on separate occasions in the district were not killed by dogs, despite police investigations finding they were.

"I just couldn't comprehend it."

And while he, like others, stop short of criticising the police investigation there was a thought in the small rural community that someone has gotten away with murder.

But now documents released under the Official Information Act reveal dogs were collared for the crime, despite police initially believing it was a gun that delivered death to the animals on the night of Friday, June 20, 2014.

But no obvious entry or exit wounds could be observed near the shattered skulls.

Nor were any bullet casings found, or gunshots heard on that night or the next when a further 120 sheep were found slaughtered.

Police returned to the scene and found two dogs: a nine-month-old Rottweiler pup and a terrier, in a nearby paddock.

The dogs had no blood on them, or signs they were involved, and were returned to their owners.

Police were now concentrating on the killing being the work of an offender. They allege the person placed a foot on each animal's head while they were held to the ground by a dog. The sheep were then shot.

An identity or motive of a person involved in the killing was unclear, with Stackhouse at a loss.

"It made no sense."

Nor could John Dodd offer any explanation when he found 28 dead sheep on his property the following weekend.

Police inquiries confirmed his sheep were killed in the same manner as those from Stackhouse's property, with no bullets, casings, tyre prints, or footprints found.

By this point police believed a suppressed rifle was used, due to the proximity of the killings to each property.

On Monday June 30, the same two dogs, a rottweiler and a terrier, were found walking along some disused rail tracks though the Dodd farm, near the paddock where the killing took place.

The dogs were again inspected, but no blood was found and they were once again returned to their owners.

The massacre of sheep on two Ngapara farms sparked "high emotion and anxiety within the community", and made national headlines, the official police report said.

"Ngapara sheep shooter 'pure evil'"said one headline, and "40-year trail of unsolved crimes under a full moon", said another.

And as pressure mounted to find the culprits, some residents even supplied the names of possible suspects to police, the report noted.

But police still had no motive, bullets/casings/gunshot residue, or even the sound of rifle shots heard at the time of both incidents.

That lack of evidence coupled with the same pair of dogs found near each scene made police re-examine their initial finding.

And that pointed the finger at the rottweiler and the terrier as the killers of the 215 sheep.

OTHER SCENARIOS

But while a dog would normally attack legs, throat/chest, it was "difficult to comprehend" how a dog's bite could take hold of the large area at the top of the skull, and crush it, the report noted.

Both dogs were not working or hunting dogs, but family pets.

However police also considered whether an offender used the dogs to capture and hold the sheep "before using blunt force trauma to kill" the animal with a heavy item.

Police believed this "would have been a very physical and tiring exercise for an offender or offenders and I would expect it would require the offender to have a very serious motive, which if it existed, the two families would know about".

Other officers from around New Zealand contacted detectives working on the case to say they supported it being the work of dogs after similar experiences.

REPRODUCING SHOT INJURIES

A police armourer believed no casings were found due to full metal jacketed bullets being used, which did not break apart on impact.

That prompted a shooting test using full metal jacket, hollow point and soft nose rounds on sheep heads, in order to replicate the injuries.

That resulted in a neat entry wound and a much larger exit wound but no "consistent large scale fracturing of the skull as seen with the killed sheep".

Police also used a pipe to replicate blunt force trauma, and with three swings of "medium force" the officer was able to fracture the skull of the dead sheep.

Four sheep heads were taken to Invermay Research Centre, Mosgiel, to be examined by a veterinary pathologist who believed they had been killed by dogs only.

However no canine DNA was able to be obtained from samples sent to Australia.

THE TWO DOGS PUT DOWN

Police interviewed the owner of the dog , and alibis were obtained for their time around the killings.

On both occasions the pets had wandered from the property on the same weekends as each sheep killing.

But police had no direct evidence linking the two dogs with the sheep killings, and after seeking a legal opinion, found there was insufficient evidence to proceed with a prosecution of the owners.

The dogs have since been voluntarily put down by their owner.

Stackhouse had talked to the owners of the dogs, who remained disappointed the pets were fingered as culprits.

"No one can believe they did that much damage."

People in the community were still concerned over the killings, but they acknowledged there had been no more incidents.

"There's a bit of doubt around because we haven't got a conclusion, police have closed their case but it is still a mystery about what happened that weekend."