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Mathew Arrowsmith's body was found after reports he'd been struck by a vehicle on State Highway 65 in Tasman in the early hours of August 29.
He was found between Maruia Saddle Rd and Pea Soup Rd in Shenandoah, Detective Dan Shields said.
"We continue to piece together a timeline of Mr Arrowsmith's movements from the Friday night until Saturday morning and we've spoken to a number of people passing through the area at the time," Shields said.
"We are now trying to identify the occupants of a later-model silver sedan that travelled north from Springs Junction to Murchison between 12.30am and 1.30am that Saturday morning.
"We are hoping the occupants of this vehicle may be able to assist with any sightings of Mr Arrowsmith at that time."
If you can assist, or may have some further information you have not passed on to police, please get in contact via 105 and quote file number 200831/0720.
Alternatively information can also be provided anonymously via Crimestoppers on 0800 555 111.