High Court Justice Francis Cooke agreed that a Bill of Rights breach had occurred, saying it did not matter that the shooting was accidental and not deliberate.
He said the officer who discharged the shot, known as Officer Z4, failed to observe minimum standards of firearms safety.
The judge also said there were "systemic" failures in the conduct of the AOS at the time, along with a general lack of standards, demonstrated by the fact that Officer Z4 and others had the wrong type of bullets loaded into their .223 M4 Bushmaster rifles.
Officer Z4's rifle was loaded with training rounds because, contrary to protocols, they had not been replaced with standard rounds after the last training exercise.
Training rounds are designed to disintegrate into tiny pieces on impact, to minimise the damage done to whatever they hit.
"As it happened, this particular failure may have saved Mr Pere's life," Justice Cooke said.
The court was told that Officer Z4's rifle, held in a sling, had brushed against the holster of his pistol, releasing the safety catch. As he stepped forward to help lift Pere off the ground, a buckle on his safety vest caught on the trigger and the rifle discharged.
Pere was taken to hospital with shrapnel from the disintegrated bullet through his back, chest and neck, and suffering from blood loss, a collapsed lung, and injury to blood vessels. He was in hospital for a month.
The judge said that Officer Z4 had received only a conditional pass from an AOS selection course in 2010, and was supposed to have received additional one-on-one training, but this had not happened.
Justice Cooke said Officer Z4 had failed to observe minimum firearms safety standards in at least two respects – by not unloading his weapon or handing it to another officer before approaching Pere, and in not obeying the "cardinal rule" that a loaded weapon should always be pointed away from people.
Forster had sought $250,000 compensation for his client, based on penalties awarded under health and safety laws.
However, the judge agreed with the Crown's counsel, Austin Powell, that health and safety law did not apply, had a different legislative purpose, and that the penalties awarded under it were not relevant.
The judge awarded $20,000 in compensation, based on the amounts awarded in other human rights cases.
Officer Z4 was charged with careless use of a firearm causing injury after the shooting, but was acquitted by a jury in the Napier District Court in 2016.
