Rodney Boatswain shot and killed great-grandmother Helen Dawson Key through her front door because he believes she convinced his mother to change her will "unfavourably" to him, a court has heard.
On Thursday, the NSW Supreme Court heard for the first time the alleged motive behind the execution-style shooting of Mrs Dawson Key, 75, at her home in Toongabbie, in Sydney's west, on November 19, 2014.
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 Mrs Dawson Key, and applied for bail on Monday.
Justice Robert Beech-Jones granted Mr Boatswain bail because it is likely he will die shortly before or after his trial as a result of his terminal liver cancer, and he is innocent until proven guilty.
The court heard Mr Boatswain, who appeared in court via audio-video link from Parklea jail, had an 81 per cent chance of dying within five years of his first treatment in mid-2014.
The prosecution case is circumstantial and alleges Mr Boatswain's motive was his long-standing belief that Mrs Dawson Key "was somehow responsible for his mother altering her will unfavourably to him".
Reita Boatswain died in November 2012.
In a series of interviews with police, Mr Boatswain admitted he held a "grudge" against Mrs Dawson Key but he consistently denied any involvement in her death.
Justice Beech-Jones said Mr Boatswain had "shown cause" as to why his detention awaiting trial was unjustified and there were no "unacceptable risks" that weighed against granting bail.
Mr Boatswain will be held in virtual home detention in a property he co-owns with his brother Maurice in Glenwood.
He will only be allowed out of the house in the company of his wife, Julie Boatswain, to attend the police station, legal appointments, Centrelink and medical treatment.
Justice Beech-Jones said motive alone was not enough to establish a prosecution case but, in this circumstance, it was particularly pertinent because Mrs Dawson Key's "peaceful life made it difficult to conceive of anyone who would want to harm her in such manner".
The court 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 using sticky tape.
A car similar to his Maroon Toyota Camry was captured on CCTV footage near Mrs Dawson Key's home before and after her death.
A neighbour also reported seeing a Maroon Camry leaving her driveway seconds after a "bang".
A committal hearing will be held on September 25.
