But for two days in October 2013, aged-care nurse Garry Steven Davis began injecting elderly SummitCare Wallsend residents with lethal doses of insulin.

Then, the man who refers to himself as "Prince Garry", texted his colleagues to accurately predict which residents were going to die next.

Davis, 29, faces the possibility of life in jail after he was found guilty in Newcastle Supreme Court on Wednesday of the murder of Gwen Fowler, 83, and Ryan Kelly, 80, and the attempted murder of Audrey Manuel, 91.

Davis hung his head in the dock and wiped away tears as Justice Robert Allan Hulme delivered his verdicts, the culmination of a four-week trial, 14-month police investigation and three years of uncertainty and distress for the families of the three victims.

There was no direct evidence, no eye-witness and no incriminating CCTV footage. But Justice Hulme was left with no doubt that Davis was the murderer after he was able to piece together the prosecution's circumstantial case and eliminate all other visitors and staff to the facility on the weekend of October 18 and 19, 2013.

But a motive for the killings remains unknown.

After the verdicts, Ms Fowler's eldest daughter said she was "appalled" at the standard of care at SummitCare Wallsend.

"I want to emphasise what a nice person my mother was, she did not deserve to be treated like something that could just be discarded," the woman said.

"She was just a really lovely person, people liked her, she was special."​

"Mum was at SummitCare to be looked after and cared for, but instead they had complete disregard for her.

"It was disgusting."

Justice Hulme rejected alternative theories, suggested by Davis's defence, that more than one person could have been responsible for the crimes, that a resident could have injected the victims or that an intruder could have broken into the facility to carry out the acts.

He noted Davis had access to insulin, had recently injected other patients with insulin without authorisation and was found with syringes and information about insulin when he was arrested.

He also said Davis had the opportunity, that he knew the residents and had texted his colleagues with information only the murderer would know.

"In relation to the accused there are the various circumstances which I have just reviewed, many of them being unique to him," Justice Hulme said. "None, on their own, establish his guilt, but when regard is had to their combined force I am left with no doubt."

The conviction was the result of a "painstakingly detailed" 14-month investigation by Strike Force Correa detectives, which included poring over 37 hours of security-camera footage from five CCTV cameras and taking hundreds of statements, Justice Hulme said.

During his closing address, defence barrister Chris Watson had been critical of the scope of the investigation, suggesting the detectives should have conducted a more thorough forensic examination of the facility and tested more rigorously for types of insulin.

But Justice Hulme labelled these propositions "unrealistic" and said the time and effort put into the investigation was "considerable".

Crown prosecutor Lee Carr also praised the work of police and said the verdict was a relief to the victims' families.

"I'm just pleased for the families," Mr Carr said after the verdicts.

"I think [Justice Hulme] is right, it was a very, very good investigation.

"When you start with 319 people, including well over 100 civilian visitors, it's a massive task.

"The families of the victims are just a nice group of people who desperately wanted to know what happened."

Detective Sergeant Matt Faber, the lead investigator on the case, commended his team.

"We are obviously very happy with result today and we hope this decision helps bring a sense of justice, relief and closure to the families of the victims involved in this matter," Detective Sergeant Faber said.

"I would also like to publicly acknowledge the professional work of the core investigators, detectives Darren Evans, Graham Galbraith and Dain Barr and our analyst Donna McNamara.

"Without their tenacity and dedication to what was a very difficult, complex and protracted investigation today's result would not have been possible."

Davis will face a sentence hearing in Newcastle Supreme Court on December 12.