A Taranaki officer failed to properly investigate a crash involving an off-duty colleague, the Independent Police Conduct Authority (IPCA) has found.
The crash in November 2015 occurred when the off-duty officer, travelling north on State Highway 3, tried to overtake a truck.
A woman in another car had to swerve to avoid a head-on collision and suffered minor injuries to her face and hand as a result.
The driver initially received a warning, and the woman complained to the IPCA, saying he was being treated favourably.
The authority found the investigation into the crash was substandard. A breath test had not been carried out, witness statements were not taken correctly and there were no photographs of the scene.
The IPCA said the investigating officer did not manage the conflict of interest appropriately and the five-month delay in charging the officer with careless driving was unacceptable. The off-duty officer was convicted and fined $400 and ordered to pay $130 in costs, but did not lose his driver's licence.
Acting Central District Commander Inspector Sarah Stewart said she accepted the case was not managed appropriately.
But she said the authority did not find evidence suggesting the investigating officer's decisions were as a result of bias or favouritism towards the off-duty officer.
But Inspector Stewart said the IPCA did not find any evidence that suggested the investigating officer's decisions were made as a result of bias or favouritism towards the off-duty officer.
"Police holds our staff to account under the law like any member of the public, and we have processes in place to ensure this happens," Inspector Stewart said.
"As the IPCA report notes, an internal review conducted by police has identified performance issues which have been dealt with."