A spate of police shootings in the last year is because too many firearms get into the wrong hands, the Police Association says.
Police previously believed Mr Sous was shot three times, but a post mortem found Mr Sous was shot in the torso and shoulder. Officers were searching for the third bullet.
It was the seventh police shooting - and fourth fatal one - in 18 months.
The Independent Police Conduct Authority (IPCA) is worried about the number of shootings and will now lead a special investigation into the issue.
IPCA chairman Judge Sir David Carruthers said the IPCA wanted to ensure force was used within well-understood limits.
"Suddenly, and it may not be statistically relevant, but in a short time we had more shootings than we've ever had before - and that was a concern, not just for me, but for all thinking New Zealanders. So it's an opportunity for us to look at all of them, see if there are any patterns or themes and report publicly on those."
Police Association president Chris Cahill said the shootings were not because of a change in police approach or trigger-happy officers.
The problem stemmed from more than 50,000 firearms, including military semi-automatic weapons, entering the country each year, a number of which are stolen or sold to offenders, he said.
"A large number of firearms are out there in the community legitimately, but then they are subject to burglaries, thefts or they are purchased by people and sold illegally to criminals."
Mr Cahill said firearms were not decommissioned, so it was unusual to have so many new ones imported.
In some cases, officers had no option but to shoot an offender, Mr Cahill said.
He said there was no shoot-to-kill policy, but there were techniques in place to disarm offenders, which could result in death.
"Officers are trained to shoot in the centre of the visible mass because if they have made the decision that they need to shoot, it's to ensure that person is totally disabled and unfortunately that often results in death."
Mr Cahill hoped the government would tighten rules on firearms this year after a Parliamentary inquiry was launched in 2016.
Police Commissioner Mike Bush said lethal force was always the last option available to frontline police officers.
He was concerned by people with firearms confronting and shooting at police.
When officers killed someone in a shoot-out, it was a traumatic experience for families and friends of the victim, but also the officer, he said.
Clarification: This story has been updated to correct a figure provided to RNZ from 20,000 to 50,000.