When taken over the last 10 years, the rate of fatal shootings is 11 times higher in New Zealand than in England and Wales - or six times higher dating back to 1990.
Specialist firearms lawyer Nicholas Taylor said the high rates of police shootings were the result of poor weapons training, a shoot-to-kill policy, and a police culture which put risk-taking ahead of de-escalation.
But Police Commissioner Andrew Coster said New Zealand's social problems were a major factor.
"If we look at gangs, if we look at family violence, if we look at youth crime and youth suicide, if we look at challenges around mental health, so New Zealand has its own context that is quite different from England and Wales."
RNZ data analysis shows at least eight of the people fatally shot by New Zealand police had received mental health treatment and others had undiagnosed or untreated mental health issues.
Coster said high rates of gun ownership - which he said was six times higher in New Zealand than in England and Wales - was a contributing factor.
But RNZ data analysis shows Norway has a rate of gun ownership similar to New Zealand's but half the number of fatal police shootings.
In New Zealand, many victims of police shootings weren't armed with guns, and some not armed at all.
The police watchdog, Independent Police Conduct Authority (IPCA), has completed investigations into 35 of the 39 people shot by police.
Those records show that six of the 35 people police killed were not holding a weapon at the moment they were shot and 14 did not have a firearm.
Among those victims was Halatau Naitoko, an innocent 17-year-old courier driver, who was accidentally shot and killed in January 2009, while driving on Auckland's Northwestern Motorway.
A coronial inquest later found the two members of the Armed Offenders Squad, who accidentally hit Naitoko while shooting at fleeing offender Stephen McDonald, lacked marksmanship skills, training and experience.
David Cerven, a 21-year-old Slovakian man shot by police in Auckland's Myers Park, was also unarmed. Cerven was holding his fingers in the shape of a gun when police killed him in August 2015.
RNZ data analysis of the 35 IPCA investigations into police shootings shows 10 of those killed were shot in the back, or from behind, at least once.
Among those was Jerrim Toms, a 29-year-old mentally ill Auckland man, whose mother had called police for help after he relapsed with bipolar disorder.
Toms was fired on four times by two officers as he walked towards them with a machete at 4am on a deserted highway near Puhoi, north of Auckland in March 2018.
He turned and ran after the first four shots but was fired on eight more times, with one bullet hitting him in the lower back. The last bullet was fired after he had dropped his machete and was nearly 15 metres away from the two officers, who fired 12 shots in total.
In 25 of the 35 cases, the person killed had not injured another person before being shot. In eight cases they had damaged property. In 17 shootings the person killed had not done any damage at all.
Shargin Stephens, a 35-year-old Rotorua man who had been bail checked by police 64 times in 36 days - as late as 2.15am and 3.49am - was shot dead in July 2016, after smashing the windows of a patrol car with a weed slasher.
Stephen Bellingham, a 37-year-old Christchurch man, had also smashed car windows when he was fatally shot in September 2007, after he advanced on an officer with a raised hammer.
Coster said even offenders without firearms could quickly become a danger.
"If they're armed with a machete or with a bat, or similar weapons, you have a very small window of time in which to defend yourself or to defend someone else before that person will be on you."
Non-lethal force, such as batons, pepper spray and Tasers, were often not safe options in those circumstances, he said.
"Taser has an effective range of 7 metres. But there's every chance that at 7 metres, you won't hit on your first shot and you've only got two shots."
In all 35 investigations, the IPCA has ruled that the police shootings were justified.
Chair Colin Doherty said the IPCA ruled they were justified on the basis of self defence in the final moments of the incident, but said in multiple cases the police put themselves in a position where firearms were the only option.
"Was it reasonable for police to have been in that situation? And that's an entirely different scenario. Should there have been better containment and cordoning for example, is that a better option?"
RNZ's data analysis shows that in seven of the 35 fatal police shootings investigated by the IPCA the police "escalated" the conflict and put themselves into a dangerous situation.
In the Bellingham case the police officer "made a decision that placed him in a confrontational position", the IPCA investigation into the shooting said.
"In doing so he reduced the options available to him and found himself in a position of having to immediately protect himself and possibly members of the public."
Taylor said there was a culture of "let's go and get 'em" in the New Zealand police.
Taylor worked for the Cerven family on the Myers Park shooting of David Cerven, who was unarmed but had told police he had a gun and was wanted on aggravated robbery charges.
"It was a situation where the police arrived and described themselves as 'tooling up' and within two minutes of the police arriving, he was shot dead in a flurry of bullets."
Police were also criticised by the IPCA for poor command and control in the Toms case, where two officers fired thinking they were the only officers at the scene. In fact there were six other patrol cars and seven other officers there.
"There's always the same pattern emerging," Taylor said. "The containment isn't properly done and the only option that seems to be viable is an aggressive approach towards the person who is acting in an unstable way, rather than trying to de-escalate and calm the situation down."
But Coster said frame-by-frame analysis after the event was very different from the heat of the moment.
"If you're in a situation where you are fearing for your life, the body's natural response is tunnel vision, the adrenaline goes, fine motor skills perish and you're… it's a fight or flight situation."
The IPCA has no power to prosecute so it is up to police to determine whether charges will be laid against an officer in a fatal shooting.
Police have never laid homicide charges against one of their officers.
Christopher Stevenson, the co-founder of the Defence Lawyers Association, said it was "profoundly unlikely" that the police had never been at fault in any of these shootings.
"The citizen is killed, their life has been taken and they are held to have been at fault in every one of those cases. I find it highly questionable."
Just once has a serving police officer come before a jury on a murder charge - but that took a private prosecution from the family of Steven Wallace, a 23-year-old man who was shot in Waitara in April, 2000.
The officer who shot Wallace, a 23-year-old Māori man, was found not guilty in December 2002.
The majority of those shot by police are Māori, reflecting the fact that police use of all types of force - including guns, Tasers and batons - is disproportionately directed at young, Māori men.
Māori men aged 17-40 are just 3 per cent of New Zealand's population but make up 34 per cent of use of force incidents by police.
In 2021 police shot four people dead, the highest number of fatal police shootings in a year since 1990. The four police shootings in New Zealand in 2021 compares with just two fatal shootings for the entire England and Wales populations in that year.
RNZ's analysis of the data shows that New Zealand has nearly eight police shootings per 10 million people, compared to zero for Finland, 0.3 in England and Wales and 2.4 in Australia.
America is in a league of its own with nearly 31 police shootings per 10 million people.
RNZ's investigation, which will also look at whether the IPCA is fit for purpose, comes as debate intensifies over whether police should be routinely armed.
Currently two Glock pistols and two Bushmaster M4 semi-automatic rifles are locked away in police vehicles, but the police union said members overwhelmingly supported carrying guns on their hips.
"It's not that the police want to be armed - it's they feel they need to be armed," union president Chris Cahill said.
But Coster is holding out against the wishes of front line officers.
"I've taken quite some criticism for my view on this, which is I do not believe that being a routinely armed police service will make our people safer and I'm confident it would lead to worse outcomes for the public."
The commissioner, however, refused to rule out arming police in the future.
"I would never say never, I have to keep an open mind according to the environment that I'm seeing in the risks as they are."