Glen Turner's murderer Ian Turnbull sentenced to 35 years

Justice Peter Johnson sentenced 81-year-old Turnbull on Thursday morning to a minimum of 24 years in jail for the "terrifying and shattering" murder of the Office of Environment and Heritage (OEH) compliance worker on a remote laneway, at Croppa Creek on July 29, 2014.

In the NSW Supreme Court in Sydney, Justice Johnson said it was a de facto life sentence for the elderly farmer, who has a life expectancy of just eight years in jail.

Mr Turner's wife, Alison McKenzie , as well as his family, friends and OEH colleagues watched on as the sentence was handed down.

During a judgement spanning an hour-and-a-half in front of a packed courtroom, Justice Johnson said he did not accept Turnbull had shown genuine remorse for the murder, or detaining Mr Turner's colleague Robert Strange at gunpoint for more than 20 minutes. 

Turnbull showed no emotion as the sentence was read out and only nodded once and waved at his wife, Robeena, seated in the front of the court. 

The sentence means Turnbull would not be eligible for parole until 2038, but Justice Johnson accepted he would die in prison before then.

Turnbull was found guilty of murder late last month after a five-week trial where the jury heard the shooting followed years of tension over illegal land-clearing.

Turnbull pleaded not guilty to murder but guilty to manslaughter on the grounds of substantial impairment due to mental illness, but the jury rejected Turnbull's defence, after one day of deliberations. They found him guilty of the more substantial charge of murder.

The defence had maintained Turnbull's major depressive order was caused by years of tension over illegal land-clearing on the family's properties at Croppa Creek.

A farmhand alerted Turnbull that Mr Turner was near his family properties, before the lifelong farmer drove to Talga Ln, Croppa Creek in the early evening of July 29, 2014.

Turnbull confronted Mr Turner, who was with OEH colleague Robert Strange, and then shot Mr Turner in the neck.

He then chased him around a car for at least 22 minutes and fired a number of shots before shooting Mr Turner in the back - the shot which proved fatal.

Mr Strange told the trial he had pleaded with Turnbull to put the gun down before the farmer got in his car and drove home, where he was arrested by police.

During the trial, Turnbull gave evidence that he intended to kill Mr Turner when he hunted him down near his property and chased him around the car.

Turnbull has been in custody since the night of the murder.