Chambers addressed media from the Auckland City Police station at midday.
He gave his apologies to Cerven's family and friends and said it was a "tragic outcome".
"I am very pleased that the authority has found the shooting of David ... was justified."
No police officer ever wants to come to work and shoot someone, he said.
"I support my staff and I support the decisions they needed to make ... that night.
"David told us that he was in Myers Park and we could go there to collect him.
"It was dark and there was members of the public moving around.
"They located David and started talking with him. Our appeal was for David to come back to the police station so we could talk with him."
Cerven had left victims very traumatised in the three aggravated robberies, Chambers said.
He did not agree with officers to return to the station and then he told them he had a gun, Chambers said.
"Appropriately armed staff arrived and moved close to David, but at a distance that was keeping them as safe as possible.
"We again appealed for David to surrender and told him that we were armed."
Police asked for him to safely surrender, "but he continued to refuse" Chambers said.
"My staff made the decision to move towards David."
It was a "courageous decision", he said.
"David immediately advanced on my staff ... and moved his arms out in front of him as if he was about to use a firearm ... the one he said that he had.
"They made the ultimate decision to use lethal force to protect themselves, their colleagues and the public.
"It was a tragic outcome that has affected David's family and friends, but also my staff."
Chambers said "there was always things to learn" but the "key thing here is that the use of lethal force was justified".
Points highlighted by the IPCA report that police could have reacted differently before such force was required were easy to make in hindsight, said Chambers.
"It's always easy in hindsight to work through different options ... but my staff have my support and I have stayed in contact with them over the last year."
The officers were both still employed, but the shooting had "taken a toll on them" and would likely do so "for the rest of their lives".
"They are family people," he said.
When asked his opinion on eight shots being fired, Chambers said: "In this situation there was some distance between David and my armed staff, it was dark, he was moving quickly ... there was a possibility that some of those shots may have been lost."
Chambers said police had stayed in close contact with Cerven's family in Slovakia.
"It has been frequent and will continue to be until the situation is resolved.
"Let's face it, they have lost a son. It's a tragedy. But we have responsibilities as police officers to do what we can to keep ourselves and the public safe."
'Police should not be there to kill'
Friends of Cerven say they refuse to accept the report's findings.
Victoria Safronova told the Herald from Canada that justice has not been served for her friend.
"Police should not be there to kill people, even when they are saying people are trying to commit suicide.
"It is the same as if someone was jumping off a bridge and the police came and they pushed him and they say, 'Oh well he wanted to die anyway'.
"We were hoping that there would be some justice, the officers that shot him should be in jail. They killed a person."
She said friends had gathered in Canada, where Cerven lived for some time, to remember the anniversary of his death last month.
"We all gathered here and remembered him and it is still a shock that this happened.
Honestly, I still can't believe that that happened, we miss him a lot."
His Kiwi workmate Dan Smith said Cerven never had a gun so police should have taken extra measures before firing.
"If anything they should have wounded him, then once they spotted a gun, maybe taken more drastic actions."
He said Cerven was a "family-oriented" guy who sent money home to his parents and was pursuing a career in kickboxing.
He said Cerven often talked about how he had nothing.
"I think he was just depressed in the end because he had an injured knee. He was a professional kickboxer, then once his knee got injured, that was his career over."
'He had committed a crime, but his sentence was not supposed to be death'
Yousuf Moghini also spoke to NZME from Canada, where he met Cerven at a kickboxing gym in 2012.
"He was always a happy, smiling, funny guy. Everyone really liked him and he was really talented, especially for his age.
Moghini said kickboxing was the way Cerven made his money, he started fighting professionally at the age of 16.
"That's how he made a living, and got the money for his family."
"He was very talkative, everyone knew him in the gym in a very short period of time. Within three weeks he won a tournament, but I think it was his charisma, it was something special."
He was still reeling from the shooting.
"I was absolutely shocked that David would do such a thing. I knew he was going through financial difficulties but I didn't know how bad it was. He wanted to do something with his life because Slovakia is really economically in bad shape.
"Then when I heard that I was very shocked. For me there was no warmup, all I heard was he was shot. Then when we started digging deeper we heard that he was in financial trouble, that he couldn't pay his surgery off so he took a loan and the bank charged him a lot of interest."
He could not believe the officers were found to be justified in their shooting, he said.
"It's unbelievable. New Zealand is known to be one of the more peaceful and tolerant countries and is regarded as very safe and police there is known to handle things calmly but they totally took this the American way.
"Police were supposed to be more prepared. They are supposed to save people. Yes he had committed a crime, but his sentence was not supposed to be death."
Cerven came to New Zealand to make a better life for himself and his family, but instead he lost it all.
"I think he thought he was going to make enough money trying to pay back his surgery. He went through this, his girlfriend said he was crying a lot which is not something David does - he went through hell training and fighting.
"There are two types of fighters, there are meat heads and there are those who are smart and strong at heart and he was one of those. He was a really genuine guy, it was just a bad time and he made some bad decisions."
New report findings
In the decision, the IPCA has stated the two officers who shot and killed Cerven were justified.
"However, the actions of the officers, in deciding to immediately approach and challenge Mr Cerven while he was engaged with other unarmed officers, precipitated Mr Cerven's response," said authority chair Judge Sir David Carruthers in his decision.
The decision stated that 25 minutes before he was shot, Cerven called police asking them to meet him in Myers Park to talk about three aggravated robberies he was suspected of committing.
The first four officers who went to the park did not have firearms.
They began talking to Cerven who did not comply with their requests to come down from a hill he was on, show his hands or lie on the ground.
A short time later Cerven told them he had a gun, said the decision.
"Two armed officers entered the park with their firearms ready to use, quickly approaching Mr Cerven and yelling at him to get on the ground.
"Mr Cerven did not comply.
"Instead, he took his hands out of his pockets and appeared to clasp them together, making it look like he had a firearm in his hands. Both officers simultaneously fired a number of shots at Mr Cerven, who died at the scene."
The shooting was therefore justified, ruled Sir David.
"The Authority accepts that the two officers believed Mr Cerven had a gun, feared for their lives and in the circumstances, according to law and Police policy, were justified in shooting him.
"However, the Authority is also of the view that the focus of the two officers was on the risk Mr Cerven posed to the unarmed officers at the scene and not on a complete assessment of the situation.
"In acting as they did, the two officers did not give sufficient weight to the risk members of the public were exposed to, or whether it was necessary to immediately engage Mr Cerven."
There were four main things the officers did not do:
• Move closer to Cerven and cover the unarmed officers while they continued to talk to him and tried to negotiate his surrender;
• Take over negotiations from the unarmed officers;
• Delay the arrest of Cerven by continuing with negotiations until the park could be properly cordoned and Cerven contained;
• Find out whether AOS was going to be, or had been, called.
Furthermore, Sir David ruled that the two officers did not advise the communications centre of their intended approach.
"Their failure to do so meant that neither the communications centre nor the four officers present in the park were aware of their plan and it was not approved by the dispatcher, who at that time had control of the incident. As the four other officers were unaware of the plan, they had limited time to retreat and take cover."
Sir David said: "The public must have confidence that police follow law and policy at all times - particularly where lethal force is involved. In this case, the Authority accepts that the officers were justified in shooting Mr Cerven, but has found that some of their actions leading up to the shooting were wanting - to the extent they precipitated the response that led to his death."
Police communications centre staff responded appropriately to Cerven's 111 call, the ruling said.
"Once Mr Cerven told police he had a gun, the dispatcher acted correctly in attempting to cordon as many park entrances as possible and in ensuring armed officers were sent to the scene. It also finds Mr Cerven received all reasonable assistance from police after he was shot."
The shooting of David Cerven
At the time of his death, Cerven was a suspect in three aggravated robberies on the North Shore.
Following his death, three separate investigations were launched.
They were: A criminal investigation against the two officers in which no charges were laid; an internal "Practise, Policy and Procedure" report and today's IPCA report.
The Coroner was yet to announce the date of an inquest.
However, in a minute released to lawyer and blogger Graeme Edgeler, Coroner Katharine Greig raised the possibility that Cerven's death was "self-inflicted".
Greig said it was "currently reasonable cause to believe the death was self-inflicted, though this is in no way a concluded view on the matter."
Police Association head Greg O'Connor said cases of "suicide by cop" were often suspected, but difficult to prove.