One of the men who shot 33 dogs in a bloody massacre runs a store advertising pet care.

Russell Mendoza entered his neighbour Rowan Hargreaves' Wellsford property with another man on Monday and killed 23 pups and 10 adult dogs. He was adamant one or more of them had fatally mauled his fox terrier days before.

Yesterday, SPCA investigators broke down as they described the horrific scenes they saw on Mr Hargreaves' 5ha block, where he lives in an old truck. The society says charges under the Animal Cruelty Act are likely.

Mr Hargreaves, who kept at least 40 dogs in a large steel cage and old car wrecks, was still in shock yesterday over the slaughter.

"If you had your family shot, how would you feel?" he said. "Even though they were dogs, they were my family. Life goes on but it's not the same."

Mr Hargreaves is keeping about eight surviving pups - including four only three days old that hid under another dog, which perished - in his mechanical workshop in Wellsford.

Mr Mendoza would not speak to the media yesterday. A friend at his home said he was preparing a statement with his lawyer to explain his side of the story. It had not been issued late last night.

The friend said he had had to disconnect his phone because of malicious calls from the public.

Mr Mendoza and his wife run Home & Garden Wellsford, which advertises pet care. Mr Hargreaves questioned his choice of occupation.

"He's supposedly an animal lover. He runs the local pet shop. Where is the logic?"

SPCA investigator Sascha Keltie, who inspected Mr Hargreaves' property, said she was "confronted by a scene not unlike a massacre".

Bullet entry and exit wounds on some of the dogs indicated they had not died instantly, and blood trails were consistent with an injured dog moving.

In a cage where eight adult dogs had been shot through the grating, six were in a corner piled on top of one another as if they had been trying to protect themselves. Another dog near the entry of the cage appeared to have been shot in the eye.

All surfaces in the cage were covered in blood.

Opposite the cage was a van wreck where two adult dogs lay dead. They appeared to have been killed with a single gunshot to the head. One of them had sheltered the 3-day-old pups.

Most of the other dead pups had been placed in a pile near Mr Hargreaves' truck covered by a tarpaulin. Two lay under vehicles nearby.

The pups were killed last, having seen the dogs in the cage and van slaughtered.

"I was in shock at first but I knew I was there to do a job. I had to get past the emotions," said Ms Keltie. "It's not until I get home at night that it comes back to haunt me."

Mr Hargreaves has admitted that he found one of his dogs attacking a sheep a day before the slaughter. He destroyed the animal, and another with similar colourings.

Rodney District Council spokesman David Anderson said the only complaint the council had received about a dog belonging to Mr Hargreaves was in 2006 and related to an incident at a different address.

All of the dogs were unregistered but the council would "wait till the dust settles" and see what the SPCA and police investigations resulted in before considering whether to fine Mr Hargreaves.

SPCA executive director Bob Kerridge said charges "will definitely be considered" once autopsy results are back and interviews are completed.

The police are also considering laying firearms charges.