Why kill the golden goose?: Qld gran trial

"Why kill the golden goose?"

That's just one of the questions posed by counsel for Steven Mark John Fennell, a one-time Macleay Island junk mail delivery man accused of bludgeoning an elderly woman to death.

The 56-year-old is on trial in Brisbane's Supreme Court, having pleaded not guilty to the murder of 85-year-old Liselotte Watson on the island in Moreton Bay, in November 2012.

During the trial, the Crown has alleged Fennell brutally and callously murdered the elderly widow, most likely in an attempt to cover up so-called financial misdeeds.

Fennell had been authorised by Mrs Watson to make cash withdrawals from her bank account on her behalf and was regularly spotted gambling at the local TAB, the prosecution argued.

But in his closing address on Wednesday, defence lawyer Adrian Donaldson questioned why his client would kill the grandmother if he had indeed been stealing money from her.

"Why kill the golden goose?" he said, noting Mrs Watson still had plenty of money in her account.

The grandmother was found dead on her bedroom floor having been struck repeatedly in the head with an object consistent with a hammer, the court has heard.

But Mr Donaldson cautioned the jury to consider the evidence carefully, telling them: "This is not an Agatha Christie story".

He said evidence from a handwriting expert that one of Mrs Watson's banking withdrawal slips appeared to have been altered - with the nominated amount jumping from $3000 to $8000 with a few extra strokes - didn't rule out the elderly woman changing her mind herself.

Mr Donaldson said Fennell did gamble but had done so for a lengthy period before Mrs Watson's violent death.

He also told the jury there was no DNA evidence linking Fennell to the murder scene and said coincidences the prosecution was using to try to implicate his client were unremarkable, given he used to run errands and drop off groceries for the elderly woman.

Mr Donaldson is expected to conclude his address on Thursday, upon which Justice Martin Daubney will begin his summing up for the jury.