Prosecutor Fletcher Pilditch is appearing for the Crown and defence lawyer Paul Mabey QC is representing Hallett.
A passing motorist found 32-year-old Mr Tahu lying in a pool of blood next to a pump in the forecourt of the Shell station.
The Saturday morning rugby referee and married father of two had suffered gunshot wounds to his head and shoulder.
He was rushed to Taumarunui Hospital but died a few hours later.
Mr Tahu's killing shocked the Turangi community and kick-started a major manhunt, but it remained a cold case until late 2011.
Police believed it was the longest-running cold case in New Zealand's history to end in an arrest.
Hallett's trial, once underway, is expected to run for about two weeks.