RSPCA inspector Simon Evans had investigated dozens of cases of animal cruelty, but he had never encountered anything quite like the scene that greeted him in October last year.
Bumper has made a full recovery and will soon be re-homed
He was acting on a tip-off from a member of the public - Griffith Prosser had taken it upon himself to fix a problem with his dog's leg.
When he called at 35-year-old Prosser's home in Merthyr Tydfil, south Wales, the scene that greeted him was gruesome to say the least.
"I've seen stabbings, I've seen shootings - I've never seen an amputation before," he told the BBC Wales news website.
On Friday, Prosser admitted causing unnecessary suffering and practicing veterinary surgery while unregistered. It marked the conclusion to a case the RSPCA described as "extreme".
Prosser's dog was hit by a car in January 2004. He took his pet to a vet in Methyr, who said the right front leg had been paralysed and should be amputated.
But, it emerged, Prosser could not afford the vet's fee and allowed his dog, a Collie cross, to limp on the bad leg for nine months.
Bumper went on to have further surgery by a vet
Mr Evans said an animal in such a state will go through a process called "nettling".
"The dog walks on top of paw rather than the pad. It's not as padded and all the fur and skin wears away to the bone."
The leg then got infected and it was then that Prosser decided to amputate.
When Mr Evans arrived at his home he said the dog looked relatively happy, but he immediately noticed one of the front legs was badly disfigured.
"There was no bandage on it at all - it was just bare. You could even see the nerves hanging out."
Prosser admitted to Mr Evans that he had cut the dog's leg off - and explained how he had done it.
"He cut the leg off using a block saw, but there was no electricity in the house so he used it as a hand saw.
"He used a hammer to break through the last bit. There was bleeding so he placed an iron in the fire and cauterised it."
Mr Evans later found the removed leg under a carpet near the back door of the house.
A spokesman for the RSPCA said investigating extreme cases such as this could be hard on those involved.
"It's upsetting for the inspectors. I guess they just deal with it - they can't allow emotions to get too much in the way," he said.
Mr Evans took Prosser's dog to Llys Nini animal centre. A vet at the centre amputated the leg higher up the limb and Bumper has since made a full recovery.
"He's a cracking dog - a really good-natured dog," said the inspector. The RSPCA hope he can be re-homed soon, now the case has been concluded.
Mr Evans believes that if any lesson can be drawn from this case, it would be the importance of people with animals taking out insurance.
"I would really encourage people to get pet insurance - operations can be expensive. Then situations when people can't afford an operation could be avoided."