Bronson Kelekolio, now aged 17, can be named for the first time today after his interim name suppression was lifted.
He earlier admitted the brutal slaying of 22-year old Ashburton mum Sina Nerisa Solomona at her Cass St home on December 15, 2012.
Today, the High Court in Christchurch was told he has not been able to speak about what happened and his motivation remained a mystery.
The court was told that he knew his victim well.
His father and her mother lived together in an extended family and was a frequent visitor to her house, Justice Graham Panckhurst said.
When considering the minimum period he must serve behind bars, the judge said "age, immaturity is undoubtedly a matter that I must seriously consider."
He said people that age had the capacity to be rehabilitated.
Crown prosecutor Andrew McRae said Kelekolio had shown "very little remorse".
"His true motivation behind the offending ... remains unknown."
Justice Panckhurst said that he is in a state of denial, no doubt because of the "enormity"of what he did.
There were gasps of "yes"f rom the packed public gallery when the sentence of 14 years, six months was handed down today.
Miss Solomona's mother Amuella Solomona gave an emotional victim impact statement which told of having a "broken heart".
"When this happened to my daughter, I felt numb, lost for words, and made me think I was to blame for this," she said.
"My heart is in pain. I can feel the anger in my kids."
She said she would rather stay in bed now sleeping, rather than staying awake and thinking about what happened.
Mrs Solomona now felt like she had to leave New Zealand to make a fresh start.
Sina's twin sister Loretta Solomona said her sister's slaying was something she and the Ashburton community would "never forget".
She is now raising Sina's 4-year old daughter whose mum was killed by the youth the family "treated as a young brother".
"My heart is broken," she said, telling Kelekolio that she hoped one day he would apologise to Sina's daughter.
Defence counsel James Rapley said his age needed to be taken into account when considering how life he should serve behind bars.
He spoke of his school struggles, where he was immature and had low intellectual function.
He was suspended from Ashburton College for disobedience and misconduct.
From a young age, he was smoking cannabis and drinking to excess, Mr Rapley said.
He still won't talk about what happened, he said.
"We don't have any insight from him."
- By Kurt Bayer of APNZ
