The Sensible Sentencing Trust is helping the widow of Feilding farmer Scott Guy with a private investigation to find out who killed her husband.
In July, Ewen Macdonald was acquitted in the High Court at Wellington of murdering Mr Guy, his brother-in-law.
Four former police officers, who are now private investigators, approached the Sensible Sentencing Trust after Garth McVicar spoke publicly about the lack of justice for the Guy family including Scott Guy's wife Kylee.
They are working for free and trust spokesperson Ruth Money says they have access to the police files on the case.
Ms Money says the trust will not rest until whoever killed Mr Guy is brought to justice.