Archibald Prize finalist and murder suspect was penniless, jury told

She had no income, no assets, and more than $50,000 in debt including thousands owed on a credit card she had shared with her late husband Thorhammer Beowulf.

Prosecutors say her mother in law Katherine Panin had already made changes restricting the power of attorney Mrs Beowulf held over her affairs.

And on the day she died, it's alleged the 81-year-old had made arrangements to change her will so that Mrs Beowulf was no longer the sole beneficiary.

"The Crown case is that Mrs Panin was murdered," prosecutor Margaret Jones told an ACT Supreme Court jury on Tuesday as she made her opening address.

The artist Mrs Beowulf, 61, and her two sons Thorsten, 32, and Bjorn, 31, are the three accused and they have each pleaded not guilty to murder.

The circumstantial case centres around what is said to be their financial motive to kill the family matriarch. The Crown pointed also to the acrimonious relationship between the woman and her family.

Mrs Panin was living with her daughter-in-law after her son died, along with her son's de facto partner Dianne McGowan and a grandson in what was described as an unconventional lifestyle.

Ms Jones said the Beowulfs had subsisted for years by selling the assets belonging to Mrs Panin.

The funds would diminish - there was a big family to support, and all five boys went to Canberra Grammar - and the family would sell another house, or the jewellery Mrs Panin's late husband used to buy her.

It was not costume jewellery, Ms Jones said; one piece was worth more than $130,000.

Mrs Panin moved to Canberra in early 2015.

Her son died of pancreatic cancer in August that year, but there were accounts their relationship had gone cold and that she rarely visited him at the hospice where he died.

There were reports too that there were challenging aspects to Mrs Panin's personality.

By October that year the family's funds were depleted and they were relying on the sale of a Woollahra home worth more than $2 million.

Mrs Panin allegedly grew unhappy living in what was described as a cramped shoebox of a room in the Red Hill home with three other adults.

Mrs Panin - who when her husband died had to learn how write a cheque and use an ATM - began to take back some control of her own finances, the court heard.

In August 2015 she revoked her enduring power of attorney with Mrs Beowulf.

Her daughter-in-law would still hold that power of attorney, but would only be able to exercise it if a doctor said Mrs Panin was not able to manage her own affairs.

Prosecutors contend this angered Mrs Beowulf when she found out a month later.

At the time, the family was selling a home on Queen Street, Woollahra, and Mrs Panin planned to use some of that money to lease a retirement unit at the Grange in Deakin.

She also made plans to change her will, and spread the inheritance equally among her remaining family rather than to Mrs Beowulf alone.

Mrs Panin had allegedly complained that her son and daughter-in-law were financially abusive, lived off her assets, and treated her like dirt.

She allegedly went to Woden Police Station and reported an incident so that if something happened to her people would know what happened.

She is said to have told police that Mrs Beowulf had become more aggressive and overt in her efforts to take her money since her son died.

October 12, 2015, was a day Mrs Panin was looking forward to, Ms Jones said.

It was the day she was to move into the unit at Grange and regain her financial independence.

Instead her life ended at the foot of the stairs at the back of the house, her head in a small pool of blood, and a foot caught up in bird netting.

It was Mrs Beowulf who called triple zero, telling the operator she had come home to find her mother-in-law had fallen down the stairs.

Prosecutors pointed to a rug that should have been in the hallway when authorities arrived and would later become critical in the trial.

Also on the day Mrs Panin died, prosecutors said Mrs Beowulf made inquiries about a property on the south coast near Bermagui, which she later bought for $980,000.

Prosecutors said it was Mrs Beowulf who organised her mother-in-law's funeral.

Mrs Panin was cremated alone a few days later. Her family had chosen the cheapest option. No friends were invited, or even told of her death.

No one attended, the court heard. But also Mrs Panin was not fussed about having a funeral.

The trial continues.