Accused nursing home murderer had 'no motive'

NSW nursing home carer Garry Davis doesn't know who murdered two dementia patients with lethal amounts of insulin and has "no motive" for such crimes, his defence says.

The 29-year-old has pleaded not guilty to the murders of 83-year-old Gwen Fowler and 80-year-old Ryan Kelly and the attempted murder of 91-year-old Audrey Manuel at Summit Care nursing home, Wallsend in October 2013.

"Our case simply put is we don't know who did it, but it wasn't us," Davis' lawyer Christopher Watson told the court on the first day of the Supreme Court trial in Newcastle.

"There's no explicable motive for injecting insulin into three people," he said.

But text messages between Davis and a female colleague just before Mrs Fowler fell ill appear to show Davis predicting their demise, crown prosecutor Lee Carr said.

Mr Carr read a series of text messages the two sent while the colleague was at home and Davis was at work on October 18, 2013.

"Hey Garry, how's Gwen going?" the colleague wrote.

"She's blue but still breathing," Davis replied.

"LOL ok thanks. John S or Doris N?"

"Bell or Kelly," he replied

Later that day Davis texted: "Gwen gone. Audrey number three."

"Thanks," she replied.

To a different colleague the next day Davis wrote: "It is going to be Audrey."

"He was able to predict those demises ... because he was the person who had injected them with a large quantity of insulin," Mr Carr said.

Davis' defence argued the texts were "tasteless" but "not reflective of a person's intention to kill".

He told the court there were 25 other people - 20 staff and five visitors - whose movements during the two-day period were unaccounted for.

The nursing home's lax security measures added strength to the case that someone else poisoned the residents, he said.

Former Summit Care nursing home operations manager, Carolyn Tranter, gave evidence the facility had undergone a major security upgrade since the deaths.

Ms Tranter said weekend visitors were encouraged to sign a register when they arrived but were not forced.

"People are free to come and go," she said.

Keys and access cards to secure areas, such as the store room where the insulin was kept, were often shared by staff, the court heard.

Mrs Fowler, Mr Ryan and Mrs Manuel suffered hypoglycaemia and hypothermia within hours of being administered insulin, the court heard.

All three were "well liked and a pleasure to deal with", were in stable physical health at the time and had no medical need for insulin, Mr Carr said.

Mrs Fowler died within 24 hours of being poisoned and Mr Kelly died 10 days after.

Mrs Manuel survived the insulin injection and died of unrelated causes a while later, Mr Carr said.

The judge-alone trial before Justice Robert Allan Hulme is continuing.