As Glendon "Glen" Turner bled heavily and his colleague Robert Strange begged to be allowed to seek medical help, Mr Turnbull allegedly said: "The only way he is going is in a body bag".

In the NSW Supreme Court on Thursday, Mr Turnbull, 81, pleaded not guilty to murder but guilty to the manslaughter of Mr Turner on July 29, 2014 at Croppa Creek, north of Moree.

The court heard Mr Turnbull intends to argue that while he admits shooting Mr Turner multiple times and causing his death, he was suffering from a mental condition at the time which reduces his culpability from murder to manslaughter.

The Crown Prosecutor Pat Barrett did not accept the manslaughter plea, telling the court Mr Turnbull was motivated by a "personal hatred of Mr Turner" and the belief he and his family were being persecuted by government authorities over land clearing.

In his opening address to the jury Mr Barrett said the accused and the victim knew each other as Mr Turner had been investigating illegal land clearing on properties owned by Mr Turnbull's son Grant and grandson Cory since 2011.

Mr Turner and Mr Strange were employed as compliance officers for the Office of Environment and Heritage and had travelled from their Tamworth base to Moree on the day of the incident. They stopped outside the Turnbull family's properties after spotting fires, presumed to be the burning of illegally cleared native vegetation.

While they stopped to take pictures and video evidence, Mr Turnbull, having been tipped off to the officers' presence by an employee, drove up and parked behind their ute. 

He got out of his car and without warning fired a shotgun, hitting Mr Turner in the neck and chin. Mr Turner fell to his knees and began to bleed heavily before getting up and hiding behind his car.

Mr Strange will give evidence that over the next 40 minutes he repeatedly pleaded for Mr Turnbull to allow him to get his injured colleague medical help.

Mr Turnbull allegedly said Mr Turner was "ruining the Turnbulls" and "continuing to harass us and taking us to court".

Mr Strange will say he told Mr Turnbull: "Enough is enough, we are only doing our jobs" to which Mr Turnbull allegedly replied: "He isn't letting us do our jobs" and "I'll kill him and that will stop him".

As Mr Turner darted around the cars another two shots were fired, one hitting Mr Turner in the chest. He then made a run for it and was shot in the back, level with his heart. He could not be revived.

Mr Turnbull drove off, allegedly telling Mr Strange: "You can go now, I'll be home waiting for the police". 

That evening he allegedly told a friend: "I had no choice, he was ruining my family and it was never going to end".

Mr Barrett said the Crown case is that at the time Mr Turnbull intended to kill Mr Turner. He told the jury of eight men and four women it would be for them to decide if Mr Turner had any impairment and if it was enough to reduce his culpability from murder to manslaughter.

In his opening address Mr Turnbull's barrister Todd Alexis SC said his client was a life-longer farmer who has well-regarded in the community and had no history of violence. 

He said the various family properties supported his extended family including four sons and the prosecutions being bought by the authorities in the Land and Environment Court caused him significant stress and he was suffering from a "major depressive illness".

Mr Alexis said there would be evidence about the manner in which Mr Turner dealt with the Turnbulls and various farm workers regarding the subject of compliance as well as evidence about the nature of Mr Turner's surveillance activities.

He told the jury they would be asked whether Mr Turner "wore him down and caused him to ultimately lose self-control and snap".

The trial before Justice Peter Johnson continues.

smh.com.au