"It's a terrible situation. But I'm sure the decision wasn't made lightly and fundamentally when it comes to these types of decisions, the most important thing is to protect human wellbeing."
It also would have been "implausible" for a tranquiliser to be used.
"Dart guns in themselves are very rarely used these days," he said.
"Most veterinary clinics, if not all veterinary clinics in this country, don't have access to a dart gun. The only place you might find a dart gun would be in a zoo."
Tranquilisers were only accurate at close range, he said.
"It isn't necessarily very easy to sedate an animal that's on the run and in distress like that. In that situation you can actually make the problem worse because the animal becomes partially sedated. It isn't always the perfect solution it might appear to be."
Aviation Security Service (Avsec) spokesman Mike Richards said Grizz escaped while he was being loaded into the back of the agency's dog unit wagon in the public area at Auckland Airport about 4.30am on Friday.
"He managed to get air side [into the] security area when a gate opened to let a truck through," Richards said.
"The airport Emergency Operations Centre was activated and a full search was commenced.
"It takes time for it to work and in the meantime Grizz could have done considerable damage or harm to himself anyway.
"It was difficult to search as most of the time it was dark."
Sixteen flights were delayed while personnel tried to get Grizz under control.
"He did not have a permanent handler so was less responsive than a dog with a permanent handler," Richards said.
"All efforts to recover him failed.
"All of Auckland's Avsec off-duty dog handlers were called in and there was a massive effort to locate and retrieve him."
Richards said the fact that the incident took place very early in the morning did not help as it was pitch black for the first two hours and Grizz simply could not be found.
"When he was located he would not let anyone near him and kept sprinting across the runways," he said.
"We tried everything, food, toys, other dogs, but nothing would work."
The area Grizz was loose inside was "too vast and too open" to try and use mobile fencing.
"In these difficult circumstances the airport's Emergency Operations Centre team decided to have the dog destroyed," Richards said.
Police assisting Avsec were instructed to shoot Grizz.
"Avsec and the handler and members of the Explosive Detector Dog Unit are naturally quite shaken but understand the reasons for the decision," said Richards.
"Avsec will undertake a review of the incident to try and ascertain what spooked the dog and if this has any implications for ongoing training."
The estimated investment in getting a dog like Grizz to final graduation is $100,000, once it has been through all of the stages of training.
The Aviation Security Service has 32 dogs employed at airports across New Zealand.
