Tony Moore admits supplying Sean Warren with Greymouth murder weapon

George Sean Warren was sentenced at Greymouth High Court for the October 2017 murder. Photo / NZME

A mate of "cold-blooded" killer George Sean Warren has today admitted supplying the murder weapon used to execute a Greymouth mother on her doorstep.

Warren shot dead 43-year-old Hayley Jane Williams on October 22 last year as she pleaded for her life, with seven children cowering inside her Greymouth home.

The murder came a month after she lodged a police complaint that Warren indecently assaulted her in front of one of her sons.

Warren, 45, was earlier sentenced to life imprisonment with a minimum non-parole period of 17 years for what a judge described as an "inhumane and cowardly" crime.

Now, an associate of Warren has admitted supplying the murder weapon and trying to cover up his involvement in the killing.

Today, in the High Court at Christchurch, Anthony "Tony" Robert Moore pleaded guilty to unlawful possession of a .308 firearm and that between October 22 and December 20 last year he perverted the course of justice.

Moore, a 49-year-old from Runanga, was remanded in custody for sentencing in Greymouth on October 8.

Justice Gerald Nation called for a pre-sentence report and updated victim impact statements.

In June, the court heard how on a Sunday afternoon on October 22 last year, Warren walked up to Williams' Marsden Rd home – where there were seven children inside, including her own three children - with a loaded .308 shotgun under his jacket.

Williams had alleged that Warren had indecently assaulted her earlier on September 28 last year and police had him charged.

One of her children told a specialist child interviewer that a "scary man" came to his house and was trying to touch his mum and was saying "really gross" stuff to her.

With his mind "fogged by the anger he was feeling", Warren aggressively confronted Williams on her porch on October 22 and demanded she get in his car.

He aimed the gun at her and pulled the trigger but it twice failed to fire.

"Sean, I've got the five kids inside," she pleaded.

He pulled the trigger a third time.

The pathologist concluded the firearm's muzzle was less than 1m away from her at the time.

One son saw Warren point a shotgun at his mother and heard her yelling at him to leave.

He then ran to a neighbour's house for help. He did not see the actual shooting.

"While at the neighbour's house, he heard a really loud bang," the summary says.

Another of her sons hid in a wardrobe "as per a pre-arranged safety plan" regarding Warren.

"Immediately after the shot was fired he came out of the wardrobe to locate his mother deceased in the driveway, and began to scream," the court heard.

"Another child present at the address, unrelated to the victim, was in the lounge. She saw the defendant arrive and point a gun at the victim. She heard a big bang but did not see the shooting. She was aged 8 years old."

A large-scale manhunt was launched and Warren was finally found walking on Old Christchurch Rd about 33km south of Greymouth and arrested by the Armed Offenders Squad.

"F****** oaths I took her out," he later told police.

"I'm on bail for indecent assault on her, that's why I f****** shot her. She brought her f****** own death sentence on herself, man."