Scientists have been unable to help identify the object that killed Rutger Hale as he drove between Lake Hawea and Wanaka.
Hale, 22, died on October 24 as he was driving with girlfriend Danielle Oylear on State Highway 6.
An object thought to be the size of a brick smashed through his windscreen, hit Hale in the head and killed him, then smashed out through the rear window.
Police said today analysis of material taken from Hale's car showed the unknown object was made of, or contained, fragments of stainless steel of a common grade used in vehicle parts and other everyday items such as tools and cookware.
The object also had common minerals naturally occurring in soil or dirt in the South Island, police said.
The analysis by ESR and the University of Otago had provided little new information to advance the case.
"Our thoughts are with the family and friends of Rutger Hale as we are at this stage unfortunately unable to progress the case to any satisfactory conclusion," Detective Senior Sergeant Malcolm Inglis said.
The case remained open, while findings made so far would be referred to the coroner.
Oylear has said the object that killed Hale appeared to come off the back of a white utility vehicle which was travelling in the opposite direction.
The object had hit the windscreen as the vehicles, neither travelling fast, passed each other.
The bonnet of the car and the back of the utility were next to each other at that moment, with the car being slightly lower.
The utility was the only other vehicle she and Hale encountered on the trip.
Inglis said the owner of a utility had come forward, but police were unsure whether that was the vehicle they were interested in.
"We're still interested in any vehicle movements in that area," he said.
That someone did something intentionally that led to Hale's death could not be ruled out.
"Because we don't know what the object was, we never found it, we still have to be open-minded as to what did cause the fatal injuries," Inglis said.
"Until we know the full story about what killed him, it's an open case."
- Fairfax Media