Elderly man
An elderly man stands in Copacabana in Rio de Janeiro September 13, 2011. Reuters/Ricardo Moraes

A woman from Queensland has been sentenced to life in prison with a non-parole period of 21 years for murdering her 81-year-old grandfather in his Craigmore home in Adelaide's north in August 2016. The judge said the crime was dispassionately planned and brutal.

Brittney Jade Dwyer stabbed her grandfather Robert Whitwell to death. She was 19 years old at that time.

The now 20-year-old claimed to be motivated by TV series about crimes. She also intended to steal her grandfather's life savings of over $100,000, the South Australian Supreme Court has heard.

A visit to grandpa

The court also heard that Dwyer had second thoughts about killing and robbing her grandfather while driving to Adelaide from Queensland. She decided to pursue the plan.

Dwyer visited her grandfather in his home and sat with him looking at childhood photos. Then she stabbed the elderly four times. As Whitwell was dying on a kitchen chair, his granddaughter busied herself by washing the dishes.

Dwyer's girlfriend, Bernadette Burns, was also sentenced to life imprisonment for a statutory murder charge, with a non-parole period of 13-and-a-half year. She went to Adelaide with Dwyer and waited in the car putting makeup.

She reportedly encouraged her partner to follow through with the plan. One of her text messages reads "just harden up and do it,” ABC News reports.

For Justice Kevin Nicholson, it was impossible to adequately summarise the distress and profound anguish brought by the crime. "The brutal facts concerning the murder of your grandfather are relatively straightforward, however, why it came about can only be seen as very complex," he said. He initially said a non-parole period of 29 years was a suitable starting point as she believed Dwyer posed a danger to the public.

Nicholson said there were several factors that contributed to the crime, including Dwyer's personality disorder and drug addiction. Other contributing factors were her unnatural interest in violence and greed for money. She showed no emotion as she was sentenced.

Whitwell's brother, Geoffrey, said it has been a difficult time. He described his brother as a gentleman.

"You couldn't get a better brother, he was truly a real gentleman-I don't think he ever had an argument with anybody ever in his life, he always helped everybody whenever he could and he always tried to do the right thing," he said. Geoffrey said he thinks the presiding judge did an excellent job and felt the sentence was fair.