The Independent Police Conduct Authority has found a number of shortcomings and delays with a police investigation into alleged illegal hunting gave the appearance that two off-duty police officers had received favourable treatment.
But it says the police decision not to prosecute to of its own was justified.
The IPCA received four separate complaints about the delay by police in investigating and deciding whether to lay charges against two Christchurch officers, Senior Constables Gary Donnelly, a dog handler, and Dougal Adams, a scene of crime officer, who were allegedly poaching from a road in Central Otago on January 21 2016.
The complaints also alleged police treated the off-duty officers more favourably than members of the public.
The IPCA found the investigating officers should have conducted a more thorough scene examination.
"The officers did not follow standard investigative procedure or ensure that they properly understood the law on unlawful hunting,'' the IPCA report said.
"This increased the risk that the public would perceive that a conflict existed. In the end, the protracted investigation and long periods of inaction gave the impression that police were treating the off-duty officers favourably.''
IPCA chairman Judge Colin Doherty said the police investigation was "unnecessarily protracted, and only served to support the growing belief that the matter was being 'covered up' ''.
"This case demonstrates the importance of identifying incidents that are likely to present a perception of bias, and proactively managing them.
"This involves taking extra care to investigate the matter thoroughly. It also requires that the matter be resolved promptly, and that communication with complainants is clear and accurate.''
However, although the IPCA found the two off-duty officers should have received formal warnings, the police decision not to prosecute the officers was "reasonable and justifiable on public interest grounds'', the report said.
A police statement said police accepted the IPCA's findings.
Southern District Commander Superintendent Paul Basham said he acknowledged "the depth of feeling across the Central Otago community regarding illegal hunting which, to some extent, results from the inconsistency in how police have responded to such incidents in the past''.
The Southern district had already undertaken a review of the response to illegal hunting incidents, with the District Command Centre taking initial supervision of the incident attendance, he said.
A district working group has been established to provide guidance to staff.
Canterbury District Commander John Price said Senior Constables Donnelly and Adams had "undergone an employment process which has been completed.
"For privacy reasons we cannot go into these details''.
