His complaint to the IPCA is not the only one. Every year the authority receives around 2,000 about police conduct, but fewer than 100 are investigated. The rest, from the public's perspective, simply disappear.
The authority will only look into cases involving serious misconduct by police, neglect, death or serious injury. Other complaints are scrapped because they're too old or too minor. If a complaint refers to a case before the courts, the IPCA cannot investigate until the case is dealt with. But frequently it refers complaints about police back to police.
The "Roastbusters" case has been bogged down by delays in the police investigation. Last year, Beriah Hales and Joseph Parker were accused of plying teenage girls with alcohol, having group sex with them, then bragging about it online.
The IPCA received four complaints about the Roastbusters case but so far has been able to investigate only one. The authority found there was a "systemic breakdown in communication" after police incorrectly told media that no alleged victims had complained.
But until police decide if charges will be laid against the Roastbusters, the IPCA cannot deal with the other complaints.
Apart from the relatively small number of cases the IPCA investigates — 67 in the year 2012/13-one of the biggest criticisms levelled at the authority is a lack of independence because former police officers are used as investigators.
Police spokesperson for Labour Jacinda Ardern is one who has raised concerns. Ardern, a member of the Law and Order Select Committee to which the IPCA reports, wants a higher ratio of IPCA board members and investigators who are not former members of police.
She acknowledges that experience and knowledge of the internal workings of the police is beneficial but says it has to be balanced against people having faith in the system.
"Having independence and people having the ability to trust in the outcome of the IPCA is also incredibly important," she says.
Some improvements have been made by Judge Sir David Carruthers who took over as chairman of the authority mid-2012. He has employed two investigators who, although they are former British police officers, have no connection to the New Zealand police. And the authority is training another investigator who does not have a police background.
Carruthers has worked to ensure transparency by publishing the results of each investigation online.
"There is a change and I believe that to be appropriate because we're spending public money," he says. "I think the public need to see what we're doing."
Other concerns raised about the IPCA include the lack of resourcing causing a backlog of cases and long delays for people like Bentley-Payne, who has waited two and a half years for answers.
"It could have been resolved a lot quicker. The sting's been taken completely out of it," Bentley-Payne says. "There were students who were hurt quite badly and it was a traumatic situation for a lot of people who had never been involved in that kind of brutal exchange before."
The IPCA reported to the student group last July that the review had been finalised. But the report will not be released until next month — a year after the review was completed.
The IPCA is struggling with a backlog after cases such as the Urewera Raids, dubbed Operation Eight, sucked up its resources and took more than five years to complete.
This week, the authority finally released a report into the 2011 arrest of Mark Smillie, who complained after he was tasered by a police officer. Because the incident was the subject of court proceedings, the IPCA could not take further action.
The authority invited Smillie to renew his complaints after the court proceedings, which he did in July 2012. The IPCA found the police officer's use of a taser was excessive and contrary to law. The authority recommended police take disciplinary action against the officer. But that didn't happen.
Police found the officer's conduct did not warrant an internal employment investigation and opted to use extra taser training instead.
Ardern says the public need to know that when the IPCA refers complaints back to the police it is an "appropriate judgement call" rather than because of resource constraints. That judgement call matters because when cases are referred back to police the public is shut out. Police acknowledge the need for transparency but say they are bound by the law.
Although the complainant will be told about any action taken against an officer, the finding cannot be made public because the police would be in breach of its privacy and employment obligations, a spokesman says.
Decisions are reviewed by a district professional standards manager and at police national headquarters.
New Zealand Police Association president Greg O'Connor defends the decision to keep the outcomes private. Police officers' employment rights are the same as everyone else's and they need to be treated fairly, he says. "Just because they're police officers they don't give up their right to be fairly treated."
That level of privacy does not apply everywhere. In Britain, for example, victims have the right to attend disciplinary proceedings.
But O'Connor says that system is only in place because there is little faith in the British Independent Police Complaints Committee.
"Those things only start happening when the IPCA itself starts to lose credibility and the IPCA hasn't lost credibility here," says O'Connor.
But there is a case for making those investigations public, without having to publicly name police officers involved. In August last year, the IPCA publicly released a decision of an investigation into the arrest of Christchurch man John Bennett, which became the subject of an internal employment investigation.
Bennett was arrested in the early hours of December 16, 2011, while police were searching for a man accused of attacking someone in Burwood — a suburb largely deserted after the 2011 earthquake.
Bennett was woken by the sound of what he thought was an intruder and, wearing only underwear and a T-shirt, went to investigate armed with an air pistol and tee-ball bat.
Police told him to drop the weapons, which he did, and he was ordered to lie on the ground face-down. An officer pushed his face into the ground and applied pressure with his knee and foot across his back and shoulder blades.
Bennett claimed the arrest was humiliating and the IPCA later found that unreasonable force was used in the arrest, despite police not upholding the complaint.
The IPCA found that his arrest was unnecessary, unwarranted and Bennett should have been allowed to find appropriate clothing and footwear before being taken to the police station. However the officers' names were not made public.
The authority was set up in 2007 to replace the Police Complaints Authority — a body with scarce resources and even less independence that was established after the police handling of the 1981 Springbok tour.
But the IPCA has limited powers. It cannot enforce discipline on police officers found guilty of misconduct. But it isn't a power the authority necessarily wants.
Sir David says in Britain,where the police complaints committee does have those powers, the result is police officers under investigation hire lawyers and remain mum during investigations.
In contrast, police officers here are able to speak freely without fear of reprisal, which allows the IPCA to carry out its investigations thoroughly, he says.
Neither does the IPCA have the power to initiate its own investigations. However Carruthers says that not being able to start its own inquiry without a complaint "feels foolish".
In April this year Brett Makiri, a man labelled dangerous by police, walked out of a busy central city police station and escaped.
But because no one has complained, this incident won't be investigated independently.
Ardern agrees with Carruthers, saying that although cases with a strong public interest were usually the subject of a complaint, that may not always be the case.
IPCA complaints
• In the 2012/13 period, the IPCA received 1997 complaints.
• Of those, 62 were investigated by the authority. Nine reports were released publicly.
• Another 270 complaints were referred to the police for investigation.
• The remaining 1,600 complaints were disregarded because they were found to be extremely minor, had no basis, referred to historic cases or related to cases still before the courts.
The role of the IPCA
The IPCA does not have the power to initiate investigations, but it can examine cases once police have investigated or after they've been dealt with by the court system.
John Banks — The authority is evaluating complaints about the police decision not to pursue charges against Banks. The police said there was insufficient evidence that Banks knowingly submitted a false electoral return during his 2010 Auckland mayoralty bid. It received complaints but kept a "watching brief" during the case.
The IPCA's decision to evaluate the complaints came after Banks was found guilty this month.
Urewera Raids — Operation Eight — It took five years for the IPCA to publicly release its decision on Operation Eight. It was unable to report during court proceedings.
The authority received multiple complaints about police ill treatment in the Eastern Bay of Plenty while they investigated military-style training camps.
The IPCA found police were justified in executing the warrants, but that road blocks set up in response were unlawful, unjustified and unreasonable.
Roastbusters — Last month the IPCA released a report on police communication after the Roastbusters incident. The authority found there was a police misunderstanding that resulted in incorrect information being given to media. It found there was no conspiracy or deliberate cover-up.
The IPCA is still examining the criminal investigation into the Roastbusters but those findings will not be released until police complete their own investigation. No charges have been laid.
