Police are reopening an investigation into the death of Libby McKay, after her mother raised doubts about how she died.
Libby McKay, 27, was driving home from a party with her boyfriend Mike Brown in Christchurch in June 2013 when she fell out of the ute, sustaining serious head injuries.
The couple attended a party in West Melton, where Ms McKay drank whisky and vodka and smoked cannabis.
After she fell out of the vehicle, Mr Brown picked her up off the road, drove to their home in Hornby and then called an ambulance. She died five days later in Christchurch Hospital.
The initial inquest found police had insufficient evidence to consider prosecuting Mr Brown or anyone else.
Ms McKay's mother, Pauline Webby, did not believe the boyfriend's explanation and contacted crash experts.
National MP for Nelson Nick Smith was approached by the family and wrote to Police Commissioner Mike Bush urging another inquiry into Ms McKay's death.
"The police commissioner's given a commitment to urgently and comprehensively review the case ... that of course would include the technical report that I've provided the police commissioner with from the family," he said.
Dr Smith told Morning Report he wrote to Mr Bush after reading the report which raised concerns about the lack of evidence in the case.
"Pauline Webby ... came to me in Nelson with the new evidence, the expert evidence, and it was very conclusive that the explanation that was given by the boyfriend in how Libby died simply was 'untenable' [according to the report].
"Supposedly [while driving] at 60 or 70 kilometres an hour in Halswell [Junction Road], she fell out of the vehicle and ragdolled down the road.
"Yet there were no soft tissue issues, bruises, there was absolutely no abrasions on any of her clothing and there was no evidence at the site where the accident supposedly occurred."
In 2015, Mr Brown was issued with a witness summons to attend the inquest, but travelled to Australia.
He wrote a letter saying he was unable to attend due to his feelings of distress over the death of Ms McKay.
Dr Smith said comments made by Libby's friends regarding her relationship alongside the boyfriend's departure was also of concern.
"I was also quite unnerved by the friends of Libby saying that there was examples of domestic violence, that she had made comments that she wanted to end the relationship and then sort of compounded on to that, it is a very bad look and I think it actually raises wider issues, that the partner shot through to Australia and under our law is not able to be required to appear at the coroner's hearing.
"There was a number of instances and comments from friends of Libby that sort of just raised concerns, so I would describe this as a suspicious death that's well worthwhile [an] inquiry," Dr Smith said.
At the inquest, witness accounts of the couple's relationship varied, with a friend of Ms McKay saying she had complained several times about Mr Brown's actions, while a man who lived with them said they were very affectionate.
At the time of the hearing, coroner David Crerar said another inquiry into Ms McKay's death was needed because there were unanswered questions for Mr Brown.
Dr Smith reiterated the complications around the inquest since Mr Brown was in Australia, and added on to that the fact people cannot be extradited for a coroner's hearing.
"At the coroner's hearing, great frustration that the key witness was not able to provide evidence," Dr Smith said.
He said the question for police will be whether there could be sufficient evidence in the report for a more serious charge and extradition.