"That's somebody at a senior level, probably around detective inspector, overseen by the detective superintendent, just to make sure everything's done correctly."
Burdett said it will be no different to any other internal investigation, and will help eliminate any emotional connections.
He also suspects McLean might be treated harsher than the average alleged offender, as often police aren't softer on their own.
"You're dealing with perhaps another investigator or another cop who knows all the tricks and traps."
Senior officers from outside the Southland district, Inspector Steve Wood from Dunedin and Detective Superintendent Peter Read from Canterbury, have been called in to oversee the homicide investigation.
Southern District Commander Superintendent Paul Basham said the move was important to ensure an impartial investigation.
