Wellington man pleads guilty to murdering woman and sexually assaulting her 12-year-old daughter

Warning:  this article contains graphic details which may upset some audiences.

A Wellington man has admitted he sexually violated a 12-year-old girl, after a deadly attack on her mother with a mallet.

Joseph Borton called the police the following day and told them he was a peeping Tom.

On Monday, Borton pleaded guilty to a raft of charges - murder, sexual violation, indecent assault, wounding with intent to cause grievous bodily harm, theft and burglary.

Outside court, the officer who led the investigation spoke of his relief.

"Police are particularly pleased that guilty pleas have been entered and we can continue to provide support and welfare to the victim," said Detective Senior Sergeant Warwick McKee.

A case summary outlines how Borton, who lived on Lemnos Ave in Karori, attacked his victims with a steel mallet he'd stolen as they did laundry at a nearby house.

He surprised the 12-year-old in the hallway and hit her in the head. She tried to escape, but he hit her again.

The girl's mother heard the scream and came to help but was struck repeatedly in the head, causing heavy bleeding.

Borton then undressed the girl and violated her, while the mother groaned in pain, before heading home for a shower and returning later.

Police say they've wrapped support around the young victim since the attack and she's had surgery to reconstruct her skull.

"The girl appears to be recovering, we continue to provide support and welfare to her and she has a good family network," said McKee on Monday.

Sixteen hours after he attacked the mother and daughter, Borton called police to admit to the murder.

He said he'd planned to incapacitate the mother to carry out the sexual offence on her daughter.

Borton will remain in custody until his sentencing in October.