Walcha murder trial: Crown finishes closing address in Natasha Beth Darcy's trial for murdering Mathew Dunbar in 2017

Crown prosecutor Brett Hatfield finished his four-day closing address on Monday afternoon, claiming the jury was open to find Natasha Beth Darcy had murdered Mathew Dunbar on or about August 2, 2017.

Darcy, 46, has pleaded not guilty to Mr Dunbar's murder on his 'Pandora' property near Walcha, but has instead argued she assisted his suicide.

Mr Hatfield told the jury Darcy was "setting the scene" and "spreading information or a false trail" to friends, exaggerating his depression for "a staged suicide".

"Exaggerating or talking about how bad the deceased was, it comes from the accused, not from him," he said.

He said the Crown's argument was "this was a case of a murder, rather than suicide", because this "emanated from the accused, and she lied about it, we say repeatedly".

He pointed to searches on an iPhone on syncing and retrieving deleted information from Apple devices, including one that read 'the police retrieve deleted Facebook messages on phone'; and said in early August 2017, Darcy was "researching and preparing her answers for the police the next day".

The Crown submitted the jury was open to find some of her answers in a police interview might be "false or manufactured evidence".

He said Darcy's phone was seized by police in August 2017 and "before the toxicology [results] was in she looked them up".

Mr Hatfield said police discovered the Acepromazine in the gastric contents of Mr Dunbar on August 24, 2017, but did not notify Darcy until November. He claimed there was evidence of Darcy searching for the drug on August 9.

Mr Hatfield told the jury this was "indicative of her knowledge" of the drugs "because she administered [them] to him".

He said the "lengths that the accused go to and the specificity of the searches ... to research and investigate those matters" was "not explained" by mere curiosity or desire to address rumours around town.

"[It's] indicative of her having a consciousness of guilt of having murdered the deceased," he submitted.

Mr Hatfield said Darcy was a "cold and calculating person who was determined to kill" Mr Dunbar and take his wealth.

It's the Crown case that Darcy sedated her partner with a cocktail of prescription drugs and sedatives in a Nutribullet before gassing him in his bedroom, in order to inherit the multi-million dollar farm.

He said the jury would need to consider there was "no evidence of any communication between the deceased or the accused" on any methods of suicide; and a lack of any evidence of any searches made by anyone else other than the accused.

He submitted Darcy was captured alone on CCTV at a Tamworth cafe watching videos of a suicide method.

Mr Hatfield submitted to the jury that "she pursued the deceased online" and she stood to gain financially substantially ... she had the motive."

He said toxicology results showed none of Mr Dunbar's usual medication was found in his gastric contents, but rather he said the jury was open to find "the accused gave the cocktail of drugs" to Mr Dunbar.

"It's consistent with the searches on the phone," he said.

Mr Hatfield pointed to an old high school friend who supported Darcy after the death. He claimed Darcy wrote two letters to her which "seek to direct [the friend] to lie and give a version that will explain those matters" of depression and suicide at the murder trial.

He said the woman was "shocked and emotionally affected of her receipt of those letters".

"The fact that the accused asked [this friend] to lie for her and give false evidence ... [shows] her conscious of her own guilt on the charge of murder," Mr Hatfield said.

He submitted Darcy "offered to give [the friend] as much as you need if she would lie to for her in her murder trial", and this was "not only brazen, but persistent".

The defence will give its closing address on Tuesday when the trial resumes.