The Independent Police Conduct Authority says the way the police handled a woman's complaints about her former partner in the months before she was killed was grossly inadequate.
The IPCA says Ashlee Edwards complained twice about Jimmy Akuhata breaching a protection order, but police did not act against him.
Ashlee Edwards' body was found in a Whangarei stream in July 2012 and Akuhata has been charged with her murder.
The authority says she laid two seperate complaints in May 2012, both of which included sufficient evidence to prosecute Akuhata, but he was released without charge on both occasions.
Superintendent Russell Le Prou said he accepts police failed to protect Edwards and the officers involved have been disciplined.