Key Points:

The fatal shot that killed a young courier driver was fired by a police officer from the side of the Northwestern Motorway as the gunman being pursued threatened a truck driver with a sawn-off .22 rifle.

Herald inquiries to police yesterday revealed that armed offenders squad members on the side of the motorway fired towards the truck and the centre of the road.

The van, in which Halatau Naitoko was sitting, was in the line of fire. Altogether the police fired five shots, one by an officer with a Glock pistol and four by two armed offenders squad members with M4 rifles.

One of the M4 bullets killed 17-year-old Halatau. Other shots hit the truck and shrapnel wounded driver Richard Neville and the pursued gunman.

Last night, an emotional Mr Neville was in no doubt that the police had saved his life. He said the 50-year-old gunman had moments earlier stood in front of his truck and pointed the gun at him to stop him.

Mr Neville, 40, said he tried to run the offender down but the man ran to the side of the truck and leaped on the back in an apparent hijack attempt.

The gunman then aimed his .22 sawn-off Ruger rifle at him through the cab window, he said.

As armed offenders squad members shouted orders to the offender, Mr Neville hit his brakes in an attempt to slam the man into the back of the cab.

The next thing he knew there was a series of shots, with glass and bullet fragments flying everywhere.

The offender later underwent surgery for his shrapnel wounds and was discharged from hospital yesterday. He will appear in the Auckland District Court today charged initially with failing to stop for police and using a firearm against a law enforcement officer.

A young Auckland couple, Kelly Simmonds and Thomas Poole, were one car length in front of Mr Naitoko's van after stopping to let officers move in front of them.

Ms Simmonds, 19, said she watched as armed police stormed Mr Neville's flat-deck truck after a series of shots and noticed Mr Naitoko's van when it hit them from behind repeatedly.

"The van nudged us and it kept nudging us forward," she said. At the time she was unaware of what had happened.

The van stopped when Mr Poole, 20, pulled on the handbrake of his vehicle.

Said Ms Simmonds: "I looked straight back and there was no one in the driver's seat and no one in the passenger's seat - that's how quickly it happened. [It was] almost as if he'd fallen aside and come off the brakes."

Ms Simmonds was shocked to learn later that Mr Naitoko had died.

Although the situation was tragic, she said, she was grateful the police had acted. "We were so close. We were in shock ... How did that happen?"

Mr Neville said he had dinner with his family last night, "celebrating life".

Police spokeswoman Noreen Hegarty said it would be weeks before the full facts surrounding the shooting were known. It is the first time police have shot dead an innocent bystander.

"The armed offenders squad had one intention and one act to perform and that was to get that man away from there as quickly as possible with minimal harm to anybody," she said.

"The only intention that all the police at the motorway scene had was to apprehend the armed and dangerous man who had sparked the whole sad and tragic saga. There was no deliberate police action towards Halatau. He was in the wrong place at the wrong time."

Ms Hegarty said investigators were working to find out which of the two armed offenders squad members had fired the fatal shot. "We don't know how many each AOS member fired until we do a formal interview."

The gunman's sawn-off rifle was found with one shell in its breech, indicating that one of "possibly many" shots had been fired.