Mr Marshall was grilled by a select committee about the police response to the case in which underage girls claimed they had been plied with alcohol and sexually abused by west Auckland teens.
Asked for his assessment of the police response, Mr Marshall said: "Certainly, the situation involving the initial response that there hadn't been a complaint and then we found there had been a complaint ... was something that we should have been sharper on in terms of communication.
"That excited, naturally, the members of the public, and we accept that.''
Police Minister Anne Tolley asked for the Independent Police Conduct Authority to investigate the police's handling of the case.
Labour police spokeswoman Jacinda Ardern pointed to a drop in public confidence in the police since the Roast Busters case, which a survey showed had fallen from 82 per cent to 76 per cent.
Mr Marshall defended this record, saying that the survey often fluctuated, had a margin of error of 3 per cent, and was roughly the same as this time last year.
The commissioner, who will soon finish his tenure, said the case was not a blot on his legacy because crime and road deaths had dropped steadily under his watch.
"I'm very bullish about what police have achieved. I think the New Zealand public is well served by this place.''
- By Isaac Davison of the NZ Herald
