Detective Inspector Scott Beard thanked police staff who have "worked tirelessly" on this investigation to get "justice for Grace".
"I also want to thank the NZ public for the messages of support they sent through the investigation for the Millane family ... it is absolutely unbelievable."
Beard referred to the killer's actions as "a senseless and needless murder".
"He can maintain his innocence, but the jury found him guilty."
"Strangling someone for five to 10 minutes until they die is not rough sex. If people are going to use that as a defence, all it's going to do is revictimise the victim and their family ... I don't believe that rough sex should be a defence."
There was "no doubt" the case had been tough for everyone involved, Beard said.
In response to questions about the killer's emotional reaction to the trial and the sentence, Scott Beard said it was not for him to say.
"It's not for me to comment on how he reacted, except that he murdered Grace Millane. That's what the jury determined and that's what he was sentenced for today."
Grace Millane: Murderer sentenced to life in prison with minimum term of 17 years