A gate connected connected to an airside security area had been opened to let a truck through and the dog chose to make its escape and run onto the airfield at about 4am.
Sixteen domestic and global flights were delayed for safety reasons at the nation's busiest airport while the animal was on the loose for three hours. Sixteen flights were delayed in the time Grizz was being recovered.
People are upset after police shot a dog on the run at Auckland Airport in New Zealand.
New Zealand Police Inspector Tracy Phillips released a statement that claimed the security service and airport staff worked for more than three hours to capture the dog, but failed.
"Our thoughts are with the AVSEC dog handler involved".
The shooting has raised questions about why a taser wasn't used.
"This is not an outcome anyone wanted, and police were only asked to be involved as a last resort".
He got to a secure area when a truck passed through a security gate.
Meanwhile, 16 flights were delayed.
Grizz was a 10-month-old bearded collie/German short-haired pointer cross on an initial airport environment socialisation programme as part of his training before undertaking block courses and assessments including the critical task of identifying explosives.
National animal rights organisation Safe said it was "appalled about the needless killing of this dog", spokesman Hans Kriek said.
The safety of the dog and people on the ground and in the air were paramount in the decision-making, an spokesperson for the airport added.
"They did everything they could, but unfortunately the dog had to be shot", she said, according to The Sydney Morning Herald.
Animal charities hit out at the decision to destroy the dog rather than first trying to contain him with a tranquiliser gun.
"Our dog teams search for any explosives in vehicle parks, navigation facilities, unattended cars and unattended items/bags, cargo, and aircraft", the website said.
Avsec said it is investigating what spooked him and whether any lessons can be learned for future training.