Davison, a 50-year-old South African based microbiologist faced trial last month on a charge of attemped murder but pleaded guilty to an amended charge of inciting and procuring suicide.
That plea was withdrawn in the High Court at Dunedin today when the Crown asked to amend the charge substituting the word ''counselling'' for ''inciting''.
Davison then pleaded guilty to the new charge which read that ''Peter Sean Romeo Davison, on or about the 24th day of October, 2006 at Dunedin, did counsel and procure Patricia Elizabeth Davison to commit suicide, in consequence whereof that person attempted suicide.
He was charged last year, 15 months after publication of his book in which he detailed the last few months of his terminally-ill mother's life and the fact that, at her request he gave her crush morphine tablets in a glass of water.
It was an act of love and compassion and Davison was complying with his mother's wishes, lawyer Roger Laybourn said. Had he resisted her wishes, Davison would never have come before the court.
The reality was that, Dr Davison, Sean Davison's 85-year-old mother, was absolutely determined "this would happen'', that her son would comply with her wishes and end her life with a morphine overdose.
And Mr Laybourn said that although Dr Davison was weak and close to death, having been on a water-only diet for over two months, she was not vulnerable in terms of willpower.
He asked that Davison be allowed to return to South Africa without a conviction to continue his work in identifying degraded DNA which assisted the the South African police to identify and prosecute offenders from the apartheid era.
Davison was also involved with the Innocence Project where, as a result of his DNA work, wrongly convicted people had been exonerated.
Crown counsel Robin Bates said it was accepted that Davison had acted out of love and compassion and not for any personal gain, that 85-year-old Dr Davison had been on a hunger strike, had asked to die and had asked others to assist her.
She was in the last days of her life but, because there was no post mortem examination, it was not possible to say if she died from the administration of the morphine overdose or not.
But contrary to what was stated in a television programme after Davison's guilty plea, Dr Davison was not in intense pain in the last days of her life.
Davison had obtained a morphine pump for her and that may have been to cover up the administration of the morphine. It was reasonable to assume Davison assisted his mother to take the morphine, Mr Bates said.
Justice French told Davison the court had to impose a sentence which held him accountable, denounced his actions and provided a deterrent to others.
There was also a need to be consistent with sentences in similar cases as well as taking into account the gravity of the offending.
The seriousness of the offence of assisting suicide was indicated by the maximum penalty which was 14 years' imprisonment.
And while there were very few similar cases and no settled sentencing policy, she took the view the offending was at the lower end of the scale and that Davison had acted out of compassion and love, not for any personal gain.
