The death of Christchurch woman Mellory Manning is one of two cold cases police are keen to crack, looking to a new DNA tool.

Police confirm they're trialling Forensic Investigative Genetic Genealogy testing, which compares DNA of unidentified suspects with genetic profiles on genealogy websites.

Mellory's brother Rob Manning says this technology is a positive step forward for everyone in society.

He says this technology has done well overseas, where it famously helped catch the 'Golden State Killer' after 40 years.

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