Several Armed Offenders Squad members called to the hostage siege in Opunake last year were reportedly drinking before the fatal shooting.
Anthony Ratahi, 46, was shot dead after he held his former girlfriend Marcelle Beer hostage at gunpoint and barricaded himself inside the Headlands Hotel for 12 hours in July.
Police have revealed to Fairfax Media that 14 AOS members were drinking before the callout. None of them was the officer who fatally shot Ratahi, or the AOS commander and Special Tactics Group commander.
About 60 police officers were called to the siege.
Police said the findings have led to a tightening of their alcohol drinking policies.
Assistant Commissioner operations Nick Perry told Fairfax the officers' alcohol consumption - which ranged from a glass of wine with a meal to five pints of beer over the five hours before the siege - came to light during a police inquiry into the shooting.
He said the previous policy was ambiguous in relation to AOS members who were not on stand-by and were responding to an emergency situation.
The policy has since been changed so that officers cannot consume alcohol within 12 hours of commencing rostered AOS duty.
The officers who had been drinking voluntarily disclosed this to the police investigation, and an employment investigation concluded that although the officers had breached the code of conduct by consuming alcohol prior to the callout, the ambiguity of the rules meant no sanctions were imposed.
Mr Perry said the inquiry had shown the shooting was justified, and the officer who fired the fatal shot complied with procedure and policy.
Police said the findings will be reviewed by the IPCA and coroner.
