'Widow of Walcha' sentenced to 40 years for murdering farmer Mathew Dunbar

Natasha Beth Darcy has been sentenced in a New South Wales court to a maximum of 40 years jail for murdering her partner Mathew Dunbar in 2017.

In June last year a jury found Darcy guilty of sedating and murdering the farmer after she was made the sole beneficiary of his multi-million-dollar merino property at Walcha, near Tamworth, on the state's northern tablelands.

She sedated him with a cocktail of drugs - blended in a NutriBullet - before gassing him.

READ MORE: Twelve things defence relies on in murder trial of Natasha Beth Darcy

At the time of Mr Dunbar's death on August 2, 2017, Darcy told police and friends the 42-year-old had died by suicide using a combination of helium and drugs.

Darcy's murder trial heard how she pressured Mr Dunbar to change his will months after they met on a dating site, and of her extensive web searches on how to kill him undetected.

Between February and August 2017, Darcy Googled hundreds of different ways to murder Mr Dunbar.

On the night of his murder, possibly after she had killed him, she used his phone to search "Does helium show up in an autopsy?" Some of the searches include:

• 11 toxic wild plants that look like food
• How to commit murder
• 99 undetectable poisons
• Plastic bag suffocation
• How long after suicide is there a crime scene?
• Can police see deleted text messages

Mr Dunbar also helped care for Darcy's three children after she went back to jail in 2016 for breaching her parole - having served time for sedating her estranged husband Colin Crossman and burning down their family home while he slept in 2009.

Bizarrely, Mr Crossman was the first paramedic on the scene after Mr Dunbar was murdered.

Darcy is eligible for parole in November 2047.

Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14.