Barrister Simon Shamy describes the tragic murder of Ruby Knox. He represented Donella Knox who admitted killing her daughter.

In May 2016, Donella Knox sedated and then smothered her 21-year-old daughter, Ruby.

She was sent to jail for four years.

Donella had been the sole carer for her daughter Ruby for 20 years.

Ruby was severely autistic and intellectually disabled. She could not speak, was violent and needed constant care.

Mr Shamy said mother and daughter loved each other very much, and had no one but each other.

"The level of pain and suffering that Ms Knox has undergone for 20 years on her own and now for the rest of her life is unparalled in my experience," he said.

In sentencing Ms Knox, Justice Joe Williams described the case as "once in a generation" which made a life sentence manifestly unjust.

Go to this episode on rnz.co.nz for more details