He said only two people will ever know what really happened in the killer's apartment, and "one of them is dead".
"So what happened?"
By the jury's verdict, Justice Moore said, the claim of sex gone wrong was rejected.
Even the killer's second police interview, Justice Moore said, contained "demonstrable lies".
He continued to insist that Millane's death was "some terrible accident".
But Justice Moore said: "I accept that at some point you and Miss Millane must have discussed BDSM practices."
Some of the killer's lies to police were sprinkled with truth, which he must have known police would discover at some point from CCTV footage or other means, Moore said.
The killer will be referred to a psychologist while serving his sentence. But, the judge said, no mental health issues had been diagnosed to date.
The killer has no previous criminal convctions.
He accepted that the bruises found on Millane's arms were consistant with "restraint".
It was common ground that at some point during her strangulation she would have lost consciousness, but it remains uncertain exactly when.
"We do not know if Miss Millane struggled, she most likely did."
Earlier, Millane's mother Gillian read her statement via a video link from England. The news that her daughter was found in a shallow grave will "haunt" her for the rest of her life, she said.
She said the killer had "taken my daughter's future" and robbed her family of so many memories.
"The terror and pain she must have experienced at your hands, as a mother I would have done anything to change places with her.
"She died terrified and alone in a room with you."
Millane's parents sat through every day of the nearly three week-long trial. They tearfully told journalists after the guilty verdict they would return to England and "try to pick up the pieces of our lives".
Members of the Auckland police team who worked on the investigation were at the proceeding today, including Detective Inspector Scott Beard, who spoke to media outside court.
"Today's sentencing sees the end of what has been a long and difficult period of time for the Millane family. The impact of losing their daughter on her birthday while alone in a foreign country has been significant and no matter what the outcome they will forever have a life sentence.
"Even though their lives have been changed forever we hope with support from family and friends they can now try in some way to move forward with their lives."
He thanked police who worked on the investigation who had "been nothing but professional, hardworking and determined to bring justice for Grace".
"The sentencing today is a reflection of the gravity and ongoing impact her murderer's actions have had, not only on the family but also on people across New Zealand and the United Kingdom.
"Our thoughts and sympathies remain with Grace's family and friends as they continue to try and make sense of her senseless and needless death."
Millane, who was travelling the world, met her killer on the dating app Tinder before they shared some drinks at a few bars on the eve of her 22nd birthday in December 2018.
She died in the man's apartment in the CityLife Hotel.
The killer's defence used expert evidence and those who knew Millane to argue it was an accidental death during erotic asphyxiation.
But in court this morning, Crown prosecutor Brian Dickey said the murder displayed a high-level of brutality. Her death by strangulation was a "very personalised" way to kill a person.
Dickey said the actions of the killer after Millane's murder showed callousness, including his search for internet pornography and taking intimate photos of her dead body.
He said the killer "erotised" the murder which displayed "depravity".
But the murderer's actions didn't stop there as he tried to "cover up his tracks" and lie to police.
The university graduate would never leave the room alive - her body later found dumped in shallow grave in the Waitākere Ranges.
After hearing from nearly 40 witnesses during the highly-charged and emotional trial, the jury's guilty verdict was unanimous.
They heard how the killer strangled Millane to death in his CityLife hotel room and then took "trophy" photos of her body.
He "eroticised the death of British backpacker Grace Millane" because of his "morbid sexual interest", Dickey told them.
Police used some of the six terabytes of CCTV footage they collected to track the killer's movements across Auckland before and after he killed Millane.
His internet search history, expert witness, and those who knew the murderer's inclination to dominate women was also canvassed.
Brookie said his client had "freaked out" before later lying to police and trying to cover up the homicide.
• Top cop Scott Beard who led Grace Millane's murder investigation speaks about the case for the first time. Anna Leask reports in a special feature later today and Beard joins Heather du Plessis-Allan Drive at 5.05 pm on Newstalk ZB.