The brother of Aleksander Vojneski has told the Supreme Court his sibling appeared delusional and "didn't seem right mentally" the weekend before he allegedly stabbed his girlfriend to death in her Macgregor home.
Vojneski, 31, is accused of murdering Canberra mother-of-three Paula Conlon on March 27, 2012.
Ms Conlon was found dead on a bed in her room. She had suffered 11 stab wounds.
The Crown has spent weeks building a circumstantial case against her boyfriend, Vojneski, who struggled with mental health problems, abused the drug ice and, it is alleged, had a history of violence and knife use.
Vojneski and Ms Conlon met in a psychiatric unit, Ward 2n, at Calvary Hospital in October the year before.
Their relationship was fractured, the court has heard, and was marked by frequent break-ups and allegations of violence.
Prosecutor Shane Drumgold is alleging Vojneski was put in a pressure cooker-type scenario on the night of the murder, created by his failed attempts to get drugs on credit, his lack of money and Ms Conlon's purchase of clothes and her desire to get him off ice.
The Supreme Court trial heard from Vojneski's brother, Vladimir Vojneski, on Tuesday.
He was in the witness box all day and repeatedly answered questions by saying he could not remember or did not know.
He did recall seeing his brother on the weekend before the murder.
"He wasn't well," he said. "He just didn't seem right mentally, and he was a bit ... I'd describe it as delusional, I guess."
Later on Tuesday, Vladimir denied giving his brother a new pair of pants, a pair of white shoes, or collecting any clothing from him after Ms Conlon's death.
He also said he had never lent his white work van to his brother before. Aleksander was found inside the van the morning after the killing.
Vladimir said he left the key in a meter box at his home, and workers and friends, up to 100 in total, had access to the van.
He said he couldn't remember where his van was on the evening of March 27, 2012.
Under cross-examination by barrister Jack Pappas Vladimir was quizzed over his own use of the drug ice and conceded he was a heavy user and was using every day at the time of the killing.
Mr Pappas accused him of trying to plant a "false memory" in the mind of another witness that a key for the white work van had been left outside in the meter box for his brother.
Vladimir responded that he wouldn't influence the witness and didn't know why he would.
Mr Pappas said the only reason would have been to put his brother "in the frame" for the murder.
He accused Vladimir of giving his brother large amounts of money for drugs the day after the killing to keep him out of the way and said he didn't want his brother going back to Macgregor.
Vladimir, the court heard, had also called his brother every hour for five hours that night, something the witness said he didn't remember.
He was also questioned about his movements the day after Ms Conlon's death, when he picked up his brother from Hawker, took him to Belconnen, before later meeting him at Dickson to organise drugs and at a friend's house in Belconnen.
The trial continues on Wednesday before Justice John Burns.