Authorities believe murdered great-grandmother was directly targeted

Police believe a 75-year-old woman gunned down in the doorway to her Sydney home was specifically targeted, as they search for a witness with a slight limp.

Toongabbie great-grandmother Helen Dawson Key was found shot in the head at her home on November 20.

Police are pursuing several lines of inquiry, but are still calling for anyone with information to come forward.

"At this point detectives are still trying to establish why this great-grandmother was killed in the way she was and we are at a loss," Detective Superintendent Michael Willing told reporters.

In a statement, authorities said:

"Police do believe that Mrs Dawson Key was targeted, and that this was not a random attack. We are working on a number of lines of inquiry, which we are not at liberty to discuss."

The 75-year-old was gunned down at about 6pm in the doorway of her Toongabbie home on November 19, with forensics ruling the bullet passed through the screen door before hitting her.

Her body was found around 16 hours later by a bowling friend from the Toongabbie Sports Club.

Mrs Dawson Key had no known enemies or criminal links, and has been described as a well-liked and respected woman.

"I just cannot imagine how this would have happened, or who would have wanted to do it. She didn't have any enemies… everyone that knew her loved her," sister Narelle Window said.

"I just hope that she didn't suffer and that it was quick… that she didn't have to suffer too much."

The family today was seen packing up Mrs Dawson Key's belongings from the home she had lived in for 30 years.

Police are hoping CCTV vision captured of a man in McCoy Park, directly behind the great-grandmother's home a short time after her attack could provide vital information about her murder.

The man dressed in dark clothing and with a slight limp has yet to be identified, despite a number of calls received from the public.

He remains a person authorities would like to speak with.