Writing in a blog on the police website, Mr Marshall said despite the best efforts of the 12,000-strong force, sometimes mistakes were made - but they had to be acknowledged.
"There are lessons to be learned in the recent case." He said there had been mistakes in communication - police for days said no girl had been "brave" enough to make a complaint, when in fact a teenager had - but he did not believe that reflected a "cultural malaise" in relation to the 2007 Commission of Inquiry.
Instead, he maintained police had made significant culture changes.
"I'm confident in this because I speak to scores of people every day and travel widely up and down this country. I also receive unsolicited letters and other communications extolling police's virtues from members of the public. Many relate to people who have been helped with matters of sexual assault.
"But I repeat we can't afford to fail victims of sexual assault, and if we do the public will not forgive us. Nor should they, given the absolute importance of such investigations."
There had been an increase of 10.8 per cent in sexual offences in 2012-13, but it was encouraging people were coming forward to make the complaints.
"'And if anyone wants to talk to police about the Waitemata case, they can call 0800 OP CLOVER (0800 672 568)."
