The man who led a campaign to prove Alan Hall was innocent says it's unacceptable it's taken so long to clear his name.

The Supreme Court has quashed Hall's murder conviction.

The Auckland man spent 19 years behind bars over the violent home invasion and killing of 52-year-old Arthur Easton in Papakura in 1985.

Investigator Tim McKinnel told Mike Hosking Hall's 36 year wait for justice is extraordinary.

He says miscarriages of justice shouldn't happen, but there also needs to be processes in place to deal with such miscarriages if they do happen.

The Solicitor-General has launched an investigation into the lawyers involved in the case.

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