Three weeks after the slaying of Kevin Ratana in front of his Whanganui home, police are urging those who know something to come forward.

Police investigating the death of the 27-year-old Mongrel Mob member today issued a fresh request today for those who haven't yet spoken to police to get in touch.

Tomorrow marks three weeks since Ratana was killed in front of his home in Puriri Street.

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So far, eight men have been arrested in relation to the investigation into Ratana's death though no one have been charged with the killing. They face charges including threatening to kill, unlawful possession of ammunition and participation in an organised crime group.

Detective Senior Sergeant Paul Baskett said the inquiry had made "significant progress".

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"A number of people have provided valuable information to the investigation team and we'd like to thank them for their assistance," he said.

"However we know that there are people who have information and have not yet spoken to us. We believe those people are likely to have critical evidence relating to Kevin's death.

"For the sake of Kevin's whanau, we're urging anyone who can assist the investigation team to come forward and speak to us.

Baskett assured anyone with information would be treated with the utmost confidentiality.

The inquiry team could be contacted at 06 349 0600.

Information could also be provided anonymously by calling Crimestoppers on 0800 555 111.