The dog had been let outside just as police walked past.
Seeing two officers walk past the property, Buddy had approached, barking and "rushing" at them. Initially, the officers were able to shoo Buddy away by waving their arms.
They continued on their search for the escaper but, on their return, again encountered Buddy and pepper-sprayed him.
The dog was "just barking at them and running around", Mr Wellington said. He was being aggressive and confrontational, he concedes, but had never touched or bitten anyone.
"I couldn't get control of him. But he didn't touch anybody."
A senior sergeant called in Dog Control to come and contain Buddy. When that failed, he drew his pistol intending to shoot the dog.
Mr Wellington blocked his attempts and the officer called for back-up. The 46-year-old also tried to block another officer from shooting Buddy with a rifle, and was arrested.
Following a "full-on, out-of-control situation" - where police chased his dog around the Otara cul-de-sac - an officer cornered Buddy and fired two shots. The first, through the chest, injured Buddy. The second, from close range, went through Buddy's head, killing him.
Eight months later, defending a charge in Manukau District Court of obstructing police, Mr Wellington saw the case thrown out.
In the published court decision, Judge Anna Johns criticised the police handling of the situation.
"The dog's behaviour, in my view, is properly characterised as rushing, and on that basis I do not consider that there was a basis on which to have the dog destroyed, and on that basis I do not consider therefore that [the officer] was, in fact, acting in the execution of a lawful duty.
"I consider that the action of the police in this case was like killing an ant with a hammer."
Having failed in an earlier attempt to have the officers sanctioned by the Independent Police Conduct Authority, Mr Wellington complained again and has received an apology from Counties Manukau senior professional conduct manager Inspector T. Phillips.
"[An] investigation has found that police had no authority in law to shoot your dog and acted contrary to [the law]. Your complaint against the police shooting your dog has been upheld. I sincerely apologise to you and your family for the loss of your dog Buddy."
But the apology wasn't enough, Mr Wellington said. While police had admitted wrongdoing, they had offered no compensation and their internal investigation wasn't enough, he said.
"I want someone criminally charged. They walked on to my property ... I was protecting my dog and he was protecting me."
Counties Manukau police declined to comment on the case yesterday.