Grandmother murder was targeted: police

Homicide detectives say the shooting of a Sydney grandmother last year wasn't a case of mistaken identity but they still have no clue why she was targeted.

Helen Dawson Key, 75, was shot through the front screen of her Toongabbie home in Sydney's west on November 19.

Detective Inspector David Laidlaw said it was one of the most baffling cases he's come across.

"We are of the view it was targeted - in some way shape or form," he told reporters.

Ms Dawson Key was a much-loved member of her local sporting club and was due to attend a bowls event on the day a friend found her dead.

Police recently released CCTV footage from near Ms Dawson Key's home of a man with a distinctive limp, recorded prior to the murder.

Det Insp Laidlaw said police were still seeking assistance to identify him.

Investigators have also released footage of a maroon coloured 1990s model Toyota Camry - with distinctive orange seat covers - which was seen around the Toongabbie area when Ms Dawson Key was killed.

Niece Jenny Hitchcock said losing her aunt, who would have recently celebrated her 76th birthday, had been devastating.

"Helen has been taken from us in the most tragic way anyone can imagine," she said.

"She was very devoted to her family and passionate about her love for bowls and helping others."

Police believe Ms Dawson Key's killer would have seen her face before they fired at her through her screen door.

Det Insp Laidlaw said investigators had ruled out a case of mistaken identity, but wouldn't reveal why.