Mr Patel's family were devastated at the length of the sentence because they thought his life was worth more. "I'm not happy with three years but what can you do? That's the law in New Zealand," son George Patel said after the sentencing.
He said he would never forgive O'Brien and doubted he was remorseful. O'Brien had wanted to meet the Patel family at a restorative justice conference but the family refused.
Mr Patel wanted a longer jail term but said he wouldn't have been satisfied with any punishment for what his father had to endure.
"[For] my father's life ... any sentence is not sufficient for us. He told of promising his mother 20 years ago he would look after his father for the rest of his life.
"I hoped he would outlive me. He was disciplined and led a healthy, active life. I feel like I have lost a precious part of my life."
The manslaughter wasn't O'Brien's first offence. In 2001, in Dunedin, he was ordered to complete 150 hours' community service for threatening to kill and for assaulting a female.
He will come before the Parole Board again in February when he has completed the rehabilitation programme. He is due to be released in April.