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Former Constable Benjamin Peter McLean (48) was jailed for life with a minimum of 17 years when he was sentenced before the High Court at Invercargill this week.
His 40-year-old wife Verity "Bert" McLean had left him for his best friend Garry Duggan when the serving officer took bloody revenge.
On April 25, McLean went to the Otepuni Ave unit his wife shared with her new partner and shot her once in the head after binding and gagging her.
He then waited for Mr Duggan and shot him twice when he arrived home.
The victim, who now has a bullet lodged beside his spine too dangerous to remove, survived the attack and described McLean as an "evil bastard" at sentencing.
Court documents showed the killer had taken a bag with him containing items including handcuffs, a police radio and a wooden police-issue baton.
Police confirmed staff from outside the Southern District had conducted an independent internal review alongside the criminal investigation.
"The review did not identify any aspects of police policy or practice that could have prevented what was an unprecedented and premeditated act," Detective Inspector Steve Wood said in a statement.
However, he confirmed the parallel inquiry had made two recommendations for change, to be considered by district leadership.
• Reviewing the audit process for police radios.
• Providing additional training and information to staff on trespass by updating the police manual.
Det Insp Wood said the latter issue cropped up through an incident unrelated to the murder.
"That recommendation resulted from a previous incident involving the issue of a trespass notice in relation to Ben McLean’s property," he said.
No changes to police policy have yet been finalised.
Police also confirmed a Family Violence Death Review had been sparked by the April incident, which was standard in such cases.
The Independent Police Conduct Authority also had a role in the investigation.Case resolution manager Monica Robbers said its role was ongoing and refused to comment further.
Despite killing his wife, McLean said at sentencing that she had broken his heart and he referred to their three children as "the real victims".
Mr Duggan, whose statement was read outside court, had a different view.
"Too often these crime cases are about the murderer and not the victim and that’s always unfair," he said.
"I ask today only that we give more thought ... and more compassion to those who have been denied their lives by evil people."