The Independent Police Conduct Association (IPCA) investigation into Deputy Commissioner Wally Haumaha claims he was "belittling and humiliating" towards staff.
The IPCA began its investigation after receiving three complaints about DC Haumaha's behaviour, including claims he had bullied two women from the Ministry of Justice and Corrections who were working on a joint project with police.
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The report, released on Thursday, found his behaviour was "inappropriate and unprofessional" and "unnecessarily autocratic".
"He exhibited intimidating and humiliating behaviour," the report states.
"DC Haumaha showed a lack of judgement in expecting an autocratic management style to get the best from an inter-agency team."
It's the second review DC Haumaha has faced, after a separate inquiry led by Mary Scholtens QC looked into the process that led to him being appointed as Deputy Commissioner.
Ms Scholtens found there were no complaints made to police about Mr Haumaha's conduct, and "without a complaint there was nothing to take into account".
However she did acknowledge that his management style had come into question.
"The incidents reflected DC Haumaha's adoption of a direct police-style approach to a multi-agency project, where a more orthodox public sector approach may have been appropriate."
The two women who placed complaints about DC Haumaha's behaviour with the Independent Police Conduct Authority say their complaints about bullying were minimised.
"In 2016 we struggled to get our complaints about Deputy Commissioner Haumaha's behaviour taken seriously. We came up against impenetrable systemic barriers.
"We want to be clear: we complained," the women wrote in a statement to Newshub.
"We were never given the opportunity by the police to formalise our complaints at that time. The outcome of these complaints is that our concerns were minimised and the incidents in question were never investigated."
But this latest report finds he did act inappropriately and unprofessionally towards staff members.
Police Minister Stuart Nash has previously said he wasn't prepared to put his confidence behind Mr Haumaha until the IPCA report was complete.
"We don't want to prejudice that in any way, shape or form, so let's just wait until that's back," he told media in November.
He said the decision on whether Mr Haumaha would return to his office would be a decision for the Police Commissioner.
But National's police spokesperson Chris Bishop says his appointment has been a "debacle from the start".
"Wally Haumaha's position as the country's second highest ranking cop is now untenable," he says.
And National leader Simon Bridges agrees, calling it a "damning report".
"It was Prime Minister Jacinda Ardern who appointed Wally Haumaha. She now has to take responsibility and dismiss the man that she appointed to one of the most senior and powerful roles in the country," he says.
"It would be unconscionable for Mr Haumaha to stay in this constitutionally important role given the seriousness of the IPCA findings."
A separate review by the State Services Commission into how the different departments handled the bullying allegations is expected to be released on Thursday.
Mr Nash has been contacted for comment.