Aged-care nurse Garry Steven Davis was the only person who could have killed two elderly SummitCare Wallsend residents with lethal insulin injections over two days in October, 2013, Newcastle Supreme Court has heard. 

And Mr Davis, 29, was also the only one to predict who was going to die next in a series of text messages to two staff members.  

He faced the first day of a judge-alone trial on Wednesday into allegations he murdered nursing home residents Gwen Fowler, 83, and Ryan Kelly, 80, and attempted to murder Audrey Manuel, then 91. 

During his opening address, Crown prosecutor Lee Carr told Justice Robert Allan Hulme each of the victims were in “relatively good health” in the hours before they suddenly fell ill and were taken to John Hunter Hospital on October 18 and 19, 2013. 

He said all three were displaying symptoms of being hypoglycaemic and hypothermic. A specialist endocrinologist, on-call for both Mr Kelly and Ms Manuel’s presentations, became suspicious and requested blood tests, the court heard. “That testing was done and results showed large levels of insulin in the blood that was not naturally occurring,” Mr Carr said.

Mr Carr said the prosecution would call 25 people, who were at the aged care facility on both days in 2013, to give evidence during the trial in a bid to eliminate them as being responsible for injecting the residents, leaving Mr Davis as the only possible murderer. During his opening, barrister Christopher Watson, for Mr Davis, told Justice Hulme there was no dispute the three victims were injected with large doses of insulin. “Our case, simply put, is we don't know who did it, but it wasn't us,” Mr Watson said.

Mr Watson said despite references made by Mr Carr to fingerprint scanners and CCTV cameras, security at the aged-care home “wasn’t that profound”. “There was easy access able to be made by people coming in off the street,” Mr Watson said.

He rejected the prosecution’s claims that investigators had eliminated everyone except Mr Davis, telling the court there were 13 people who visited the facility on October 18, 2013 who police had been unable to identify. 

Mr Watson told the court Mr Kelly had been interviewed by police at John Hunter Hospital between falling ill on October 19 and his death on October 29.

“He was asked a number of questions and he told the police he was injected by a woman,” Mr Watson said.

Justice Hulme will spend most of Thursday reading medical evidence and the trial is expected to resume on Friday.