New Zealand police announced Saturday that believe the British backpacker who has been missing for a week was murdered and they will charge a man they detained earlier in the day for questioning.
He will remain in custody until Monday morning when he will appear in the Auckland District Court, police said.
"Grace is no longer alive; this is now a murder investigation", DI Scott Beard of Auckland city police said.
Prior to her dissapearance, Grace had been in contact with her family everyday and concerns were raised when she didn't respond to birthday messages on Sunday December 2.
"We still do not know where Grace is, we are determined to find her and return her to her family", Inspector Beard said.
Police have now "identified and secured a vehicle of interest".
Officers established the man was with Millane on Saturday, December 1, and that they went to a number of locations before going to the City Life Hotel.
Police said there was no suggestion Millane previously knew the man she was seen entering the hotel with, but would not speculate on how they met.
New Zealand police confirmed on Saturday afternoon they are treating the investigation as a homicide.
She had been travelling alone in New Zealand for two weeks, after a six-week trip through South America.
The body of missing British tourist Grace Millane has been found by police in the Waitakere Ranges today.
In a tearful press conference on Friday, Grace's father, who has travelled to Auckland, said the "fun-loving" graduate's family are "extremely concerned" for her welfare.
Detectives are still searching for some of Millane's belongings, including her passport, a pale pink Casio Baby-G watch and a silver necklace with a green stone in the middle, which were missing from the Base Backpacker hostel where she was staying.
"We still do not know where Grace is", Detective Inspector Beard said.
A scene examination at the Citylife hotel is continuing, says Scott.