Police in Auckland have admitted that a knife, which could have been used in a stabbing death last week, was found by a contractor clearing up the scene.
Austin Hemmings, 44, died last Thursday after coming to the aid of a woman who had been assaulted in the central city.
Two knives found in the vicinity are being tested.
Detective Senior Sergeant Gerry Whitley says police failed to find one of the knives - instead it was picked up by a contractor who later cleared the scene.
He says he is disappointed that he and his team have let the Hemmings family and the Auckland community down.
Mr Whitley says they were trying to search a large area quickly, and some of the team had not had enough sleep.
He has apologised to the Hemmings family and explained why the mistake occurred.