The Crown says a 72-year-old man, accused of killing a service station attendant almost 34 years ago in the central North Island, told his estranged wife at the time that he had killed someone.
Rodney Tahu, 32, was shot in the head and shoulder early on 16 August 1979 in Turangi and died later in hospital.
Menzies Hallett is accused of murdering Mr Tahu and his trial began at the Rotorua High Court on Tuesday.
In a brief opening statement, defence lawyer Paul Mabey, QC, told jurors that Mr Hallett admits he caused Rodney Tahu's death and they will have to decide if it was murder or manslaughter.
Crown prosecutor Fletcher Pilditch told the court the only issue will be Mr Hallett's intent: why he produced his firearm and why he pulled the trigger.
Mr Pilditch said that after the shooting, Mr Hallett travelled to see his estranged wife in Wellington and talked to her about the killing.
He said Menzies Hallett was charged with murder in 1979 but discharged, because the law meant that his estranged wife could not give evidence against him at the time.
However, a law change in 2006 allows his now former wife to give evidence.
The court was told that Mr Hallett had earlier received a letter from his wife that said their child was not going to be living in Taupo with him. Mr Pilditch said that was the catalyst which the accused reacted to that led to the killing of Rodney Tahu.
The trial is scheduled to take two weeks.