Police impartiality is crucial into the investigation into the double shooting in Invercargill, says a former top cop.
Constable Benjamin Peter McLean has been charged with the murder of Verity McLean, with whom he had three children.
He has also been charged with the attempted murder of Garry Duggan, who is in a stable condition in Dunedin Hospital.
READ MORE: Locals tell of shock
Former police investigator Lance Burdett told Newstalk ZB's Larry Williams that Invercargill Police are using an independent investigator.