The Crown had argued for an eight to 10 year jail term, with Crown prosecutor Mark O’Donaghue saying Knox had “other options” at the time, including respite care and home health support.
But Justice Joe Williams said Knox had “felt cornered into taking this most terrible action for Ruby’s sake and her own.”
“The common theme from all who knew you and Ruby was that you loved and cared for Ruby constantly, diligently, unselfishly and unconditionally. A tireless advocate with health authorities, you refused to give up,” he said.
Ruby suffered from several health concerns in addition to her autism, including spina bifida, haemorrhoids, gastroesophageal reflux disease, asthma and menstrual difficulties.
60 Minutes filmed a documentary about her in 2001, with a follow-up in 2007.
The NZ Herald reports that in the six months leading up to her murder, Ruby’s condition had deteriorated markedly and she had become increasingly violent.
Hospital records show that Knox took Ruby to emergency 10 times between February and May 2016, with fears that her daughter was in pain. Ruby had already had a metal rod surgically inserted in 2009 to treat her back.
On the day she killed her daughter, 16 May 2016, Knox received a letter from the hospital saying that doctors had been unable to locate the source of the pain.
“It seems that this letter was a trigger for your decision to take Ruby’s life,” Justice Williams said.
Around lunchtime, Knox sedated Ruby with risperidone anti-psychotic medication before suffocating her. She then took herself to Blenheim police station to make a full confession.
“I became very sure of one thing: to send you to life imprisonment for Ruby’s murder would clearly be inappropriate, or in the words of the law, manifestly unjust,” Justice Williams said.
“Your feeling that the system had constantly failed you was long held, and genuinely and deeply felt. In your mind, Ruby’s unresolved pain and the burden that placed on you… left you with no viable alternative.”
An autism advocacy group has since come out saying the sentence is “nowhere near enough,” NZ Herald reports.
But at the same time, local parents have rallied to show support for Knox, with her close friend Sharna Butcher organising a protest to raise awareness of the difficult position she was in.
"I know of parents in a similar position all over New Zealand," Butcher told The Marlborough Express. "So we're going to take to the streets and rally now, to try and prevent what happened to Donella happening again."
Read more about the case here.