A Sydney grandmother who said her firefighter grandson admitted to lighting fires was "playing the sympathy card" and cried on cue, to hide her "oppressive" behaviour towards him, a court has been told.
Joshua Bruce Staples, 20, has pleaded not guilty to several charges related to lighting scrub and rubbish fires in Sydney's west in January 2011.
He was a volunteer at the Rural Fire Service at the time of the alleged offences.
His grandmother, Veletta Heron, this week told Downing Centre Local Court Mr Staples had broken down and admitted lighting the fires during a discussion at her house in mid-2011.
Mrs Heron said the admission came after she questioned him about police surveillance evidence that allegedly linked him or his car to the scenes of the blazes.
"I love my grandson. I love him very much. But I will not lie for him, or any of my children," she told the court, at one point crying and looking across at Mr Staples.
Mr Staples's barrister, Michael Coroneos, on Friday challenged the admissability of Mrs Heron's evidence.
Mr Coroneos said Mrs Heron had put a lot of pressure on her grandson to plead guilty when he didn't want to.
Mr Coroneos said Mrs Heron put on a performance in the witness box.
"She tried to play the sympathy card, she did the whole act of crying on cue,
"This is a grandmother who cares for her grandson? I'd invite your honour to come to a different view."
He said it was possible she had some kind of "ulterior motive", because of disagreements with her daughter, Mr Staples's mother, about the case.
"It's really unclear what the dynamics of that family unit really are, or what her motives really are."
Earlier, Mr Staples completed his evidence and denied he'd decided to take his mother's side over his grandmother.
"When the family unit started to fall apart ... over the course of these proceedings ... you decided to stay with your mother and hang your grandmother out to dry," police prosecutor, Sergeant Daniel McMahon, said.
"What do you mean?" replied Mr Staples.
The court has heard Mr Staples pleaded guilty in mid-2011, but changed his plea to not guilty at the end of that year.
Sergeant McMahon said Mr Staples had told his former solicitor he wanted to plea guilty.
"No," Mr Staples said.
"The reason you did that was you already admitted and agreed with your grandmother you were guilty and you were going to plea guilty," Sergeant McMahon said.
"I strongly deny that," Mr Staples said.
The hearing continues before magistrate Michelle Goodwin.