The man who intentionally rammed a police car, rolled his Jeep, and killed a great-grandfather had collided with another car on purpose seven years before.

Cornelis Kees Klein was found not guilty of manslaughter by reason of insanity at the High Court at Auckland yesterday.

Klein was diagnosed with a bipolar affective disorder 24 years ago and is believed to have relapsed before both crashes.

Roden Plimmer, 71, of Albany was killed instantly after Klein crashed into a police car, rolled and landed on top of the great-grandfather's car in February 2010.

Seven years earlier Klein had crashed into another car driven by Glenn, who did not want his last name published.

Glenn says that after the accident "I saw him getting out and he walked towards me. He had a spring in his step ... He was smiling. I said: 'You could have killed us.'"

Glenn said Klein smiled and said: "Well, yes, I was trying to kill you."

Glenn and his friends were driving in Hamilton, on their way to a Santana concert in Auckland, when they noticed a driver "lurching" out of an intersection 50m ahead.

He remembers calling out to a friend in the back of the car to shift seats before Klein "gunned his motor" and T-boned them.

"The door looked like a crushed Coke can. There is no doubt in my mind that it would have killed him."

Glenn's car spun around and ended up facing the wrong way while Klein's vehicle rolled over.

One of Glenn's mates had whip-lash but no one was seriously injured.

Klein was convicted of assault with a weapon and reckless driving. The police summary of facts said Klein had explained that he had attempted to collide with Glenn's vehicle and other vehicles for "sexual gratification".

Glenn said that seven years later he was driving home from work when he heard Klein had been involved in a similar incident and this time someone was dead.

"It's just a bloody shame that he has managed to do it again."

Psychiatrist Dr Ian Goodwin examined Klein and told the court yesterday the 2003 crash "mirrored" the crash last year. "It is likely Mr Klein could not appreciate the moral wrongfulness of his actions."

Professor Graham Mellsop also came to similar conclusions.

He read the evidence of a witness who was in the Jeep with Klein shortly before the crash. The woman, who has name suppression, said "he was not making any sense," and "he seemed to be out of his mind".

According to a police summary of facts in the latest case, Klein told the witness he wanted to commit suicide and only let her out of his Jeep when she threatened to call the police.

Police responded and overtook Klein, who made an obscene gesture. He then chased the police car before ramming it.

The police car travelled 15m, eight cars were damaged in the crash and Mr Plimmer was killed.

Professor Mellsop also read evidence from a police officer who interviewed Klein soon after the crash.

"To Constable Richards, he said: 'I am God.' Now, most people don't go around saying 'I am God' but manic people do."

He said he believed Klein was "not capable of considering the rights and wrongs" of his actions and he believed Klein's lithium dosage was too low.

Justice Patrick Keane ruled Klein should be made a "special patient".

Klein, who was an inventor with medical technology company Klein Medical, has been sent to the Mason Clinic, where he will be placed under monitoring.

He will remain there until he is considered well enough to be released back into the community.

Justice Keane also considered a lifetime ban from driving but told the court he needed to check whether that was within his power.

Outside court, Mr Plimmer's family said they were angry no one was being held accountable for the death of their loved one.

Son-in-law Scott Graham said Klein had chosen not to take his medication at one point and had also been on a lesser dose of lithium but that was not looked at.