Grace Millane's killer would have killed someone else, if not her - investigator

The lead investigator in the Grace Millane case says he believes the man jailed for her murder would have killed eventually.

The 28-year-old man was sentenced to at least 17 years in prison on Friday.

Detective Inspector Scott Beard said he empathised with her parents, David and Gillian.

He said her killer repeatedly lied to the police, and others, and was devoid of emotion.

Beard told Checkpoint the man was a danger to the community.

"I think somewhere down the track... if you'd sat at court and heard all the evidence, all the witnesses... yeah at some stage [he would've killed someone], if it wasn't Grace."

Beard said the case struck him personally, being a father to a daughter in her 20s.

He said that made it all the more difficult supporting Millane's father when he first came out to New Zealand to search for his daughter. David Millane was the only family connection to Grace in New Zealand during the investigation.

"We [the police] were his family, his friends, his support all combined.

"It was important for me leading the investigation, doing all the media interviews, to form a relationship with him to get him through because I had to tell him every day before I told the media what was going on.

"I saw this strong, loving, family man crumbling in front of me. And that's hard."

He said the emotion of the investigation showed as he spoke to media after finding Grace's body.

"The investigation team as long as myself had worked some long hours in a short period of time. It was fairly intense. The media spotlight and pressure was really intense, from my perspective.

"I'd been telling this story in the media every day that got sadder and sadder, and was leading to what ultimately was her murder, and finding Grace."

He told Checkpoint after they found the suitcase in the shallow grave off Scenic Dr in the Waitakere Ranges, and found the body, he immediately called the family liaison officer, waited a minute for confirmation the family had been told, then was soon in front of the media.

"No time to get in the zone and prep myself. It was emotional.

"There was a sense of relief that we'd found Grace. The whole aim of the investigation was to find Grace. But the tragedy around it."

He said cases like this are never forgotten.

"There's a sense of justice has been done for Grace and her family."