Police have still not found Grace Millane’s body.

But based on the evidence they have collected so far, they have now confirmed the young British backpacker who went missing in New Zealand was murdered.

Auckland Police said they were questioning a 26-year-old man about the suspected slaying of Millane and a vehicle of interest had been secured.

“The evidence we have located so far, our scene examination, some of the CCTV footage we have, and our investigation, has determined that Grace is no longer alive and that this is a murder investigation,” Auckland City Police Detective Inspector Scott Beard said.

“Grace’s family have been advised of this development and they are devastated.”

Beard added: “We still do not know where Grace is. We are determined to find her and return her to her family.”

Millane, 22, the daughter of millionaire English property developer David Millane, had not been seen since leaving her hostel in Auckland last Saturday.

The Essex woman had embarked on a year-long worldwide trip following her university graduation.

Detectives also said several of her possessions, including her passport, are also missing.

In a tearful press conference on Friday, Millane’s father, who has travelled to Auckland, said the “fun-loving” graduate’s family are “extremely concerned” for her welfare.

Her birthday was on Sunday but she didn’t contact her family.

Investigators have been examining a scene at the hotel complex where Millane, who turned 22 on Sunday, was last seen with a “male companion” on December 1. Searches have also been carried out at the backpackers’ accommodation where she was staying.

On Saturday police released images of her necklace and watch and urged anyone who recognised the items to come forward.

Beard said: “Detectives have assessed Grace’s belongings that were found at the backpackers where she was staying.

“Several of her belongings, including her passport, are missing and police believe it is likely that Grace has these items with her.”

He said the male companion whom Millane was spotted with at the City Life hotel about 9.40pm on Saturday was a person of interest in the case,

Millane, from Essex, graduated from university in September and had embarked on a year-long worldwide trip.

After visiting Peru she arrived in New Zealand on November 20 and had been “bombarding” her family with photos as she kept in near-daily contact with her parents and brothers via social media.

Police said they had received dozens of calls to a hotline and more than 25 staff were working on the case, trawling through hours of CCTV footage to trace her movements.

“Grace is a lovely, outgoing, fun-loving, family-oriented daughter,” David Millane said on Friday.

“Grace has never been out of contact for this amount of time. She’s usually in daily contact with either her mother, myself, her two brothers, or members of the family on social media.”

Millane said his daughter arrived in New Zealand on November 20, “and has been bombarding us with numerous photographs and messages of her adventures.”

“We are all extremely upset, and it’s very difficult at this time to fully describe the range of emotions we are going through.”

Millane urged anybody who had seen or spoken to his daughter over the past week to contact police.