The man who brutally beat his 69-year-old neighbour to death and then, as she lay dying and unresponsive, sexually assaulted her twice, has been sentenced to preventive detention and life imprisonment with a minimum non-parole period of 17 years for his "callous and depraved" crimes.

Jaden Lee Stroobant pleaded guilty to murdering the 69-year-old Cunxiu Tian in her family home in January last year.

He had initially denied the offending but changed his plea on the first day of his trial in the High Court at Auckland in February this year.

Sentencing for the killer began before Justice Graham Lang at 9am today.

When asked in court this morning if he had anything to say for himself, Stroobant said "nah".

He then fidgeted and muttered in the dock throughout the hearing, at one stage turning to a detective, holding his hand in the shape of a gun and miming shooting her.

As he left the court after today's sentencing, he screamed at Justice Lang: "F**k, I can't ask for better."

Stroobant had been out of prison just 38 days when he killed Tian.

Shortly before the murder, he moved into a property next to Tian's family home.

On the day Tian died, he confronted her in her Glenvil Lane garden, before dragging her inside and subjecting her to a violent beating.

As she lay on the floor of her home Stroobant sexually assaulted her twice then tried to clean her with a towel and dishwashing liquid in a bid to remove traces of forensic evidence, including semen.

Sentencing began with the victim impact statements from Tian's daughter and son-in-law.

Throughout, Stroobant chewed gum, tried to chat to the security guards who flanked him in the dock and turned to get the attention of his mother and aunt sitting behind him.