Croppa Creek killer Ian Robert Turnbull, who murdered Tamworth-based environment officer Glen Turner, dies in Sydney hospital

Turnbull, 82, was under guard by prison officers when he died in Prince of Wales Hospital in Randwick, Sydney, on Monday.

A family friend told Fairfax Media Turnbull had suffered a stroke in prison and never recovered.

He had been taken by ambulance to the hospital from Long Bay Correctional Complex earlier this month after reportedly suffering a stroke.

“An 82-year-old inmate died at Prince of Wales Hospital [on Monday]. He had a terminal illness,” the Corrective Services NSW spokeswoman said on Tuesday.

Turnbull was sentenced to a "de-facto life sentence" of 35 years behind bars for the killing of Mr Turner, who was working as a compliance officer for the Office of Environment (OEH) near Moree in 2014.

Mr Turner's widow, Alison McKenzie, said Turnbull's death meant her family would not have to endure the torment of an appeal. 

“We will never have closure, it’s just something we are learning to live with,” she told The Leader on Tuesday.

In June 2016, Justice Peter Johnson sentenced Turnbull to a minimum of 24 years in jail for the "terrifying and shattering" murder of Mr Turner on a remote laneway, at Croppa Creek on July 29, 2014.

Last month, Turnbull had lodged an appeal of his sentence that was due to be heard on May 31.

"He died a convicted murderer and spared us from the heartache of an appeal in court," Ms McKenzie said.

"He was able to receive medical attention at his time of need, something he denied his victim, my husband Glen."

On Tuesday, Mr Turner’s sister Fran Pearce told The Leader that it was “a time of mixed emotions” for the family.

“We are relieved that the judicial process is now at an end,” she said.

“It is disappointing that the murderer died so early in his sentence without ever demonstrating any remorse for his actions and without empathy for the damage he caused to our family, friends and peers.”

Mr Turner had been investigating Turnbull for illegal clearing of native vegetation, and was carrying out what should have been a routine departmental visit with a colleague, Robert Strange, when he was murdered.

Mr Turner and Mr Strange were standing on public land near Turnbull's property at Croppa Creek when Turnbull used a hunting rifle that he kept in his ute for shooting wild pigs and kangaroos to kill Mr Turner.

Turnbull was found guilty of murder in 2016 after a five-week trial in the NSW Supreme Court in Sydney 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.

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