A terminally ill mechanic accused of gunning down a Sydney grandmother blamed her when his mother changed her will and he lost his inheritance, an inquest has been told.

Rodney Boatswain, 64, died of cancer after being charged with murdering Helen Dawson, 75, who was shot dead at her Toongabbie home in November 2014.

At an inquest yoday into Dawson's death, Sergeant Durand Welsh said she had been the best friend of Boatswain's mother, who changed her will shortly before she died of cancer in 2012.

"Rodney held a grievance against Helen for the change to the will," Welsh told the hearing.

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When questioned by police, Boatswain had denied any involvement in the murder, but conceded he held Dawson responsible for the loss of his inheritance.

She had been a keen bowls player and Boatswain told police he "had wanted to break her foot so she could not bowl", but he then said he had "got over it".

Senior Constable Sharon Neil, who was in charge of the investigation, told the inquest Boatswain was the only suspect.

"We were unable to identify any other person that could have had the motive, the opportunity or the means to kill Helen Dawson in the way she was killed that morning," she said.

Describing the murder as "cowardly and brazen", she said she believed Boatswain went to the house with the sole intent of murdering Dawson.

Dawson's relatives told the coroner how much she was loved and missed, referring to her love of bowls and her three dogs.

The coroner will deliver her findings later today.

- AAP