In the trial of Alan Hall in 1986, a crucial piece of evidence was never shown to the jury.
The person we're calling 'Witness A' told police he was certain he saw a Māori man fleeing the vicinity of Grove Road on the night of the murder.
However, based on a re-enactment they performed, police decided his testimony was unreliable, saying Witness A couldn't reliably tell the ethnicity of the person he saw.
Mike drove Witness A's route form the night of the murder three times and hired three actors of different ethnicities to run past his car at the same spot that Witness A made his sighting.
Mike had never met these actors before and based on the brief glimpse he got as they passed his car tried to guess their ethnicity.
This was similar to the test that the police conducted to check the reliability of Witness A's description of the person he saw.
Watch the video for the full behind the scenes exclusive and the results of the experiment.
See Mike's full TV exclusive on the Grove Road murder here.