But it is Mr Boatswain's diagnosis of terminal throat cancer that makes him "bitter" and unsuitable for bail while awaiting trial for the execution-style shooting of 75-year-old Helen Dawson Key, the NSW Supreme Court has heard.

Mrs Dawson Key, 75, was shot at the front door of her home in Toongabbie, Sydney, on November 19.

Her body was found the next day, after she did not turn up to a lawn bowls social day with friends.

Mr Boatswain, 64, is charged with murdering the great-grandmother, and applied for bail on Monday.

His barrister Rebekah Rodger told the court there were several factors that "showed cause" for his release on bail, including his illness, delays in the court process, his illiteracy and the weakness of the Crown case.

Ms Rodger said Mr Boatswain wanted to return to his family, to live with his wife of 40 years.

The alleged motive for the shooting was not aired in detail in court, but the Crown said he acted out of bitterness.

"We say he did it with a pistol. It's not been recovered," prosecutor Colin Shaw said.

"There's a man who is bitter. We say he's demonstrated that he can be, and has been violent.

"[Mrs Dawson Key] did not stand to benefit in any way, to gain at his expense.

"This man is ageing, dying ... and he's extremely bitter and we say he has access to firearms.

"If he's on bail, anyone and everyone connected to him is in danger."

The court also heard that a workmate of Mr Boatswain, who is a heavy vehicle mechanic, allegedly overheard him say: "I shot someone and I thought I would have been caught by now."

There is also evidence that Mr Boatswain had altered the number plate on his car, which had been repaired with sticky tape, the court heard.

Ms Rodger said Mr Boatswain, who appeared in court via audio-video link from Parklea jail, with a grey handlebar moustache, had an 81 per cent chance of dying within five years of his last treatment in mid-2014.

She said the police, who publicly distributed photos of a maroon car during their investigation, had not followed up witness reports of a champagne-coloured car driving "wildly" soon after Mrs Dawson Key's neighbours heard a shot.

Ms Rodger said a Crown allegation that Mr Boatswain now had "nothing to lose" because of his condition, and would be a danger if released on bail, did not hold up because the diagnosis pre-dated the shooting.

"Clearly the police are going to be heavily monitoring his whereabouts, and his movements," she said.

"The conditions are effectively house arrest."

Justice Robert Beech-Jones will make a decision about bail on 10am on Thursday.