The officers fired 10 shots at Donald Ineson, who later died after a bullet fragment struck him. The 56-year-old was killed after police responded to reports he was threatening his family with a firearm in November 2018.
The Independent Police Conduct Authority investigated and released its report on Tuesday, saying the shooting was legally justified.
It said Ineson's wife Joanne called 111 to report that her husband had pointed a shotgun at her during an argument.
During the call, she heard two gunshots.
A few minutes later she reported that he was shooting at the front door.
"While Mrs Ineson reasonably believed at the time that Mr Ineson had fired his shotgun at the door, a later scene examination revealed he had used an axe to break in and get the keys to his car," the IPCA report said.
"In the officers' minds, Mr Ineson was volatile and dangerous, and potentially suicidal," IPCA chair Judge Colin Doherty said.
The Authority said it would have been preferable for additional officers to attend the job, as it was dangerous to enter a property and confront an armed offender.
"However, it was reasonable for them to decide to go straight to the address given the circumstances and the urgency of the situation," the new report added.
"They feared he would deliberately crash into another vehicle, potentially killing or seriously injuring any occupant of that vehicle."
The officers said they also believed Ineson may still have had the shotgun with him and were concerned he would use it against other police officers in his efforts to escape."
But the IPCA said the likelihood of these risks eventuating was low, and that shooting at Ineson to prevent his escape in these circumstances was not justified.
However, the legal test for that situation involved assessing whether force was reasonable in the circumstances, as the officers believed the circumstances to be.
A 'good man': Widow
In a statement attributed to Ineson's wife Joanne and sent to media on Tuesday morning, the family voiced some relief at IPCA findings.
"We are relieved that the IPCA have confirmed that my husband had no time to react and did not deliberately hit a police officer who ran in front of his moving vehicle as he left his home," she said in the statement.
"However, we believe the subsequent actions of the officers at the scene, which led to my husband's death, were excessive."
"My husband will be remembered by his family, friends and work colleagues as a good man."
Officer injured
As Ineson sped off in his vehicle he struck a police officer on the leg.
"The force of the impact sent [him] up onto the car's bonnet, across the windscreen and onto the roof before he rolled off the side and onto the road," the IPCA report said.
The officer dragged himself to the edge of the road and managed to pull himself into a water-filled ditch.
Police shot at Ineson's vehicle, which then came to a stop.
More officers then arrived, including a dog handler.
No movement was seen from Ineson's car and a man driving past told police Ineson was dead.
Officers waited 18 minutes after the shooting to approach the car. Ineson could be seen slumped over the steering wheel.
Police approached the car, repeatedly stopping to call on Ineson to get out.
When they reached the driver's door, they found Ineson had no pulse, and medical assistance would be useless as the Darfield man was clearly dead.
A scene examination found six bullets had hit the back of Ineson's car and a bullet fragment struck his upper left back, causing a fatal chest injury.
Boss says cops 'brave'
Canterbury district commander Superintendent John Price said police officers acted bravely, and the decision to shoot at Ineson was not taken lightly.
"Our intention is that every situation we attend can be resolved without incident to prevent harm and ensure the safety of all those involved."
Price said the incident demonstrated the "dynamic and complex" nature of some police situations.
"Our officers acted bravely and professionally in a fast-moving, high risk situation in which they only had seconds to make a decision to take action that could prevent a volatile situation from causing harm to others."
