The trial of euthanasia campaigner Sean Davison began at the High Court at Dunedin this morning.
The 49-year-old is accused of the attempted murder of his mother Dr Patricia Elizabeth Ferguson in Dunedin in 2006.
Dr Ferguson, 85, was terminally ill.
Davison has said he gave her a dose of morphine the night she died.
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The father of two, who since his mother's death has become a campaigner for legalised euthanasia, has pleaded not guilty to attempting to murder her.
A jury of four men and eight women has been selected.
The Crown is represented by Robin Bates and Marie Grills.
They must prove beyond reasonable doubt that Davison administered a quantity of morphine to Dr Ferguson, and that his intention when administering the morphine was to kill her.
Davison is represented by Roger Laybourn. Justice Christine French resides.
Twenty-five witnesses will give evidence for the Crown, including Davison's brother Fergus Davison, a bio-medical scientist.
The trial is expected to take three weeks.