A Greymouth District Court judge doubted the existence of "mysterious Michael", but said the possibility that such a person did exist meant he had to dismiss a drink-driving charge.
Accordingly, John Raymond Sadler, 47, of Cobden, walked free from the court on Tuesday.
Sadler was found in the passenger seat but was the sole person in the car when constable Matthew Wood opened the driver's door at 11.45pm on March 18.
The constable had been parked at a give way sign when he saw the vehicle go past along Bright Street, noting that there was only one occupant. He followed the vehicle in to Blackett Street and then cruised past slowly when it pulled on to the side of the road.
The police car drove on for a further 80m - the constable checking the car in his rear view mirror - before completing a u-turn and returning to the vehicle. He did not see the doors open or anyone alight so he was confident that Sadler had switched to the passenger side, where the keys were found on the floor.