Raymond Isaac Roff, 54, appeared before Justice Desmond Fagan to learn his fate, more than three years after 33-year-old Mr Rez was killed and his body dumped at an unknown location.

Hours after Roff was sentenced, his co-accused Sarah Renea Tarrant was given a jail term of 10 years and eight months with an eight-year non-parole period on a charge of manslaughter.

She will be eligible for release in 2023 at the earliest.

The court heard Tarrant was the long-term partner of Mr Rez, but had become involved with Roff, a widower whose wife passed away after an illness in 2012.

It was his passion for Tarrant that led him to murder Mr Rez in the early hours of July 29, 2013.

Days after the pair concocted a plan, Tarrant crushed up some sleeping tablets in a serving of mashed potato, which she served to Mr Rez.

Once Mr Rez was asleep in his bedroom, Tarrant sent a text message to Roff, who came over and killed the father-of-four in an unknown manner.

The pair loaded the body into Roff’s car and he disposed of it.

"This terrible crime was an extraordinary exception to everything about the offender's character and conduct up to that date," Justice Fagan said. "His descent to murder is directly attributable to his infatuation with this young woman."

In delivering his judgement, Justice Fagan added the murder was pre-meditated and occurred in the victim's home, noting Roff still denied committing the crime.

In sentencing Tarrant, Justice Fagan noted there was substantial impairment of relevant faculties but added it was beyond reasonable doubt that the idea of killing Mr Rez originated with her.