Nearly 20 homicide cases remain unsolved across the country, according to police.

Data obtained by RNZ through an OIA reveals 19 homicide cold-cases currently open, as of late last month.

Police say cases are usually inactivated - but remain 'open' - when all reasonable lines of enquiry are completed, without resolving the case.

Detective Senior Sergeant Jaedoo Danny Kim says cases are considered resolved after someone is convicted of the offence, the person responsible is identified but has died, or when the person charged is found unfit to stand trial.

In some cases, a person charged can be acquitted of the offence, but no other person is sought in connection with the homicide.

Kim says in these instances, the case may or may not be resolved, depending on whether there is clear evidence that others are involved.

Unsolved cases put victims at risk

A homicide case going cold exacerbates the grief of those impacted by it, a victim support organisation says.

Manaaki Tāngata Victim Support manager Melissa Gordon says those who lose a loved one through homicide are at risk of complicated grief and PTSD.

She says an unresolved case puts them at further risk.

"It increases the risk again of PTSD and complicated grief, and for many people, it prolongs that grief and that trauma that they feel."

Gordon says victims can be retraumatised for years by unresolved cases.

"In the wake of a homicide, or a missing person for that matter, there are a lot of rumours and media attention that goes round the communities, and more so when there's one without a resolution.

"That type of social impact can go on for many, many, many years."

Gordon says it's important for members of the community to be empathetic to those dealing with the aftermath of a cold case.

"It's easy to de-personalise these stories, especially when they're out in the media and it's not happening to us personally.

"These are real people at the heart of these stories, at the heart of these cold cases, they're real people that are having to live with this trauma, and they're deserving of all of our empathy and support."

She also encourages those who have been victims - regardless of whether they had reported a crime - to get in contact if they needed support.

"There is always hope," says Gordon.

"In my 10-11 years experience that I've had in victim support, I see it all the time.

"I see the amazing resilience that people have, and I see them overcome the biggest of challenges, and I see them at that first moment when they think 'how am I going to live', to then being able to move forward," says Gordon.

-RNZ.