A year after the killing of Upper Hutt woman Lois Tolley, police have narrowed the list of "persons of interest" to about 12 people.
The 30 year old was killed in her Ward Street home in what police have described as an "execution-style" killing, on 9 December last year.
Investigation head Detective Senior Sergeant Glenn Barnett said despite the time that had passed police were "absolutely confident" arrests would be made and the people responsible held accountable.
He said the investigation had worked through a list of more than 130 persons of interest, and had narrowed it to about 12 people either directly involved in committing the murder, helping plan the attack on Lois, or helping the killers after the murder. The list included both men and women.
"A large amount of evidence has been collected to build up a full picture of events on the night of Friday 9 December 2016," Mr Barnett said.
"We are also gaining an increasing amount of direct or first-hand evidence needed to put this matter before the court.
"Over the course of the investigation we have spoken to at least 15 people who have direct knowledge of who planned the attack, committed the murder and actively helped to cover up the offenders' involvement."
He said up to this point they had refused to help police in a way that would help make progress in the investigation - but that attitude was slowly changing.
"A number of people [are] starting to come forward with valuable information ... However, we still need more of the people who have spoken with the offenders to contact us."
He called on people in the community who were close to the Tolley family, who hadn't spoken with police, to come forward.