A woman has told a judge of her heartbreak over the murder of her sister who was bludgeoned to death with a hammer wielded by their brother.
"I am horrified to think what she would have felt when she saw that hammer raised over her head," Rebecca Delaney said on Thursday.
She told her brother, who was sitting in the NSW Supreme Court dock: "You took away the person who meant the most to me".
Lucas Christian Delaney, 32, has pleaded guilty to murdering Gabriella Delaney whose body was not found until days after her death.
The 20-year-old visual art student was killed by her brother in June 2020 in the house they shared at Cambridge Park in western Sydney.
Delaney was arrested after presenting himself to a mental health facility a day after her body was found.
At his sentence hearing, her sister and a brother read out victim impact statements while statements from her parents and another brother were handed up to Justice Peter Garling.
Rebecca Delaney said she grew up in a broken home where her older sister Gabby was the person who gave her unconditional love and support.
The very talented artist taught her to tie her shoelaces and always remembered her birthday.
"They say home is where the heart is and I feel homeless since my sister died."
Addressing her sibling, she said: "While I have so much anger and hatred for what you did, you were once my brother, so I can only hope you take this opportunity and use the resources available to you to better yourself."
Their older brother Daniel Delaney said Gabby had been going to do amazing things with her life.
He said her dog was traumatised over her death and would not let him, or any male, approach her now.
Crown prosecutor Rossi Kotsis said Delaney had intended killing his sister, but the agreed facts were bare as to an explanation of why it occurred.
"It is the crown position the offender intentionally and repeatedly struck the victim to the head with a hammer," he said.
In one account, he said he blacked out, but in another he said he thought he used a tool on a person he was communicating with online but looked down and realised it was his sister sitting on the couch.
His barrister, Brian Royce, referred to experts assessing Delaney as having had a mental illness and his use of drugs including ice which could exacerbate his condition.
"I accept I can't walk back from the fact he was taking illicit drugs and he has a history of using them in the context of his mental illness."
He said Delaney had written a letter expressing his remorse for his offending.
Mr Kotsis said his history indicated he must have been aware of the negative effects on him of his drug taking.
Friends and family had previously encouraged him to seek drug and alcohol treatment, he said.
He will be sentenced on a unspecified date.
