She was elderly and defenceless. He was a fit and healthy young man. The reason he yesterday gave for killing her so brutally was that she "spooked" him.

Olinale Ah You, 30, was given a life sentence with a minimum non-parole period of 20 years, a sentence that places him among the country's worst killers.

He attacked 80-year-old Yan Ping Yang in her Manurewa home on June 11, 2008. She was home alone when he crept in through an open window, looking for cash.

She was startled while she was turning the television off. He battered her frail body with punches and kicks and dragged her by the hair as he tried to bundle her into a wardrobe.

During the assault he pushed a cordless telephone handset into her mouth, attempted to strangle her and banged her head against the wardrobe door before finally knocking her unconscious with a stomp to the chest.

Mrs Yang died in hospital three days later but was able to tell what happened to her from her sickbed.

The High Court at Auckland heard yesterday that Ah You had been "spooked" by the presence of Mrs Yang but Crown prosecutor Kieran Raftery said what would have spooked him more than her presence was that she resisted him.

Previous victims had not put up a fight. Last year Ah You was sentenced to 12 years' jail after pleading guilty to two charges of aggravated robbery and three charges of robbery.

Mr Raftery said he was a fit and healthy young man who could easily have escaped from Mrs Yang without inflicting such cruel injuries on her.

Justice Edwin Wylie said the murder was callous and brutal.

"You have murdered an elderly and defenceless woman in her own home and all for the rather paltry sum of $2000."

Ah You showed no sympathy to Mrs Yang and did not seek medical help for her, he said.

"In effect you left her to die."

Through his lawyer, Denise Wallwork, Ah You said he was sorry and accepted what he had done.

He knew Mrs Yang's family hated him and still had nightmares about the day he killed her. But the judge labelled the apology "cynical" and doubted he was genuinely remorseful.

He said Ah You pleaded guilty to manslaughter only when DNA evidence linked him to the house - before that he denied any involvement and even claimed he had an alibi.

His manslaughter plea came at the start of his trial but a jury decided in early April he was guilty of murder.

Mrs Yang's granddaughter Lilly Su said her family would never be the same again.

"What has happened to my grandmother has deeply traumatised and scarred my family. We are in emotional pain and we do not have the happiness we once had."

Ms Su said Mrs Yang had already bought her grandchildren wedding presents but would never be able to give them or see them graduate from university.

She paid tribute to her grandma, whom she called an inspiration. "She looked after me from the day I was born ... I miss her every day."