The man who intentionally rammed a police car, rolled his jeep and killed another driver has been found not guilty by reason of insanity.

Cornelis Klein appeared at the Auckland High Court today.

Justice Patrick Keane said that he had reviewed witness statements, a DVD police interview with Klein and had heard from two psychiatrists.

"I accept that the shared conclusion is that on the second of February, 2010, that at the time Mr Klein drove into the back of the police car and before and afterwards, he was suffering from a disease of the mind, a bipolar disorder," Justice Keane said.

Klein will be detained as a "special patient" where he will undergo psychiatric care which will include monitoring of his medication.

He will remain at the Mason Clinic until suitable for release.

Michael Roden Plimmer, 71, of Albany was killed instantly. Police allege Cornelis Klein, 50, caused the crash after becoming suicidal and "shouting and screaming".

Klein later told police he had rammed the police car on purpose because he thought they were going too fast when they passed him.

He had been driving his jeep with a woman who has name suppression when he began talking about taking his own life, the police summary of facts said.

According to a police summary of facet, Klein was driving along the Albany Expressway, north Auckland, when his "behaviour changed with him shouting and screaming".

The woman pleaded for Klein to pull over and let her out but Klein refused.

The police summary said it was not until the woman threatened to call police that Klein pulled over to the side of the road.

The woman got out of the jeep, leaving her handbag in the car but taking her cellphone, which she then used to call police.

"The defendant started to walk after the passenger, following her for about 100 metres, before he returned to his vehicle," the police summary said.

A patrol car on nearby East Coast Bays Road was first to reach Klein, arriving at Rosedale Road with lights and sirens going.

The traffic behind Klein pulled over to let the police car through and it overtook Klein on his left-hand side.

"As the police passed the defendant, he put his arm out the driver's window and made a one-finger gesture at him," the summary of facts said.

Klein then chased police at speeds of up to 90km/h.

After about 1km the police car, followed by Klein, came to a red light where police said Klein deliberately rammed it from behind at speed.

The ramming pushed the patrol car into the path of incoming traffic causing more collisions.

Klein's jeep rolled onto its side, before coming to a stop on top of another car and crushing its roof. Mr Plimmer was killed instantly.

Klein managed to crawl from his jeep and was taken by ambulance to North Shore Hospital before being discharged into police custody.

The police officers involved in the crash were shaken but uninjured.