"These animals were in pain. They were suffering."
Mr Warren, who has worked for the past three years with the SPCA as regional manager for Central Districts, said he had decided together with an SPCA Wairarapa committee member and a fellow inspector to euthanase the cats.
"I admit I was the driver behind it, but someone had to do it and you can't make that sort of decision on your own. No one person should be burdened with that. It was a very tough couple of days, bloody tough. I was devastated."
Elizabeth Marshall, who has worked as a part-time volunteer at the centre for about two years, said she had resigned after witnessing the gathering together of the doomed cats on Monday.
"He just walked in and point, point, point, point. There were strays, but some were surrendered and some had been healthy cats. Some had only been there a couple of days."
Ms Marshall, who also works as a caregiver for a young tetraplegic man, said several workers minding dogs and four volunteers working with cats were all visibly upset.
"It was the way it was done. It was too traumatic for me and I think other volunteers were thinking the same. It was like ethnic cleansing really. It was slaughter.
"It was a death camp not a welfare centre and, of course, the cats knew it. They were really subdued. They knew what was going on," Ms Marshall said.
"It shattered everyone. We talked but no one said much, we were all too shocked. There were tears. I wasn't crying at the time but the others were. My tears came later."
Mr Warren said he spoke with Ms Marshall on Tuesday and had reluctantly accepted her resignation.
"I don't blame her. It's so very upsetting for us all and it was bloody terrible," he said.
"But I'd hate to think I've started here and people are calling me a cat killer. I love animals. I wouldn't do this job otherwise. We are not a murder factory."
Mr Warren said there were about 30 cats, 10 kittens, five adult dogs and four pups up for adoption at the centre.
None of the animals now at the centre would be euthanased, he said, unless they were found to be ill and a health risk.
There were about 30 volunteers working at the centre, which would soon be partially remodelled, he said.
Operational changes would include a re-focus on "our core business" of preventing animal cruelty and prosecuting offenders, tighter rules around the acceptance of unwanted but otherwise healthy animals, the introduction of "Is This Your Cat" collars, and the founding of animal fostering hubs in towns throughout the region.
Mr Warren also planned to found a "fight fund" that could be used to care for abused animals.
