By Damon Green, ITV News North of England Correspondent
Victorino Chua was a nurse who became a killer. He was employed to help the sick and the helpless - and yet his terrible crimes caused suffering and they caused death.
He betrayed his patients; he betrayed his colleagues; he betrayed his calling.
Most murders involve a violent confrontation, a battle where life is taken by force.
But Chua's crimes were committed by stealth and in secret: tampering with the medicines which were meant to make patients well, and turning those medicines to poison.
In all, detectives discovered 22 people who were harmed in his care - many of them elderly, some of them already gravely ill. Three of them died. One was left with permanent and devastating brain injury.
Nobody knows how he selected his victims. Not all of them were known to him.
Some of them were the victims of chance - given medical products he had poisoned and left lying around, in the knowledge that they would be administered by a fellow nurse.
But now a court has found him guilty and he will spend years behind bars for inflicting pain, and death, and lasting disability on people who trusted him.
Sickness and death are facts of life in a busy hospital like Stepping Hill in Stockport. A patient who takes a turn for the worse on the ward is a sad, daily event.
But in July 2011 there was a series of events which caused panic even among the experienced carers of the Acute ward.
On the night shift of July 11th, five men on ward A1 showed the symptoms of `hypoglycaemic shock' - seen in a sufferer of diabetes when their blood sugar level drops to a dangerously low level.
Four of those men were not diabetic. Two of them, 71-year-old Arnold Lancaster and 83-year-old Alfred Derek Weaver, died.
Derek's sister, Lynda Bleasdale, told ITV News what she found when she went to visit him.
Both Derek and Arnold were the victims of insulin poisoning. So was their fellow patient 41-year-old Grant Misell.
He went into such severe shock that his brain was starved of oxygen and sustained terrible injury. And all the time, Victorino Chua was the nurse on duty, doing nothing to help.
The sudden, unexpected emergencies caused panic on the wards.
Staff quickly realised that the saline solution used in intravenous 'drips' had been tampered with, and insulin added by injection.
Insulin in small quantities helps diabetic patients to regulate their blood sugar level. But in large doses, it can cause catastrophic organ failure, and death.
Stepping Hill's first thought was that the medicines were part of a contaminated batch from their supplier. They never suspected that one of their nurses was a poisoner.
Once police were called, however, they began to analyse earlier, unexplained hypoglycaemic shocks - especially where the victim was not diabetic.
They found fourteen other examples over the previous two weeks - one of which, in the case of 44-year-old Tracy Arden, had proved fatal. She had arrived at the hospital with a chest infection. She never left.
Detective Superintendent Simon Barraclough led the investigation by Greater Manchester Police. He says Chua showed not the slightest feeling for the patients he forced to suffer and die.
"He poisoned patients," he says, simply. "He poisoned Tracy Arden and she died as a result of that and he came back on duty and he knew he'd poisoned her and he knew she'd died."
Chua's medical training, begun in his native Philippines in the 1990s, had taught him that insulin is quickly eliminated by the human body, leaving no trace behind.
He was careful to leave none of his own fingerprints on the saline drips and medicine bottles responsible.
He also knew the routine of the hospital where he worked - with such a huge turnover of medical supplies and medical tests that he believed nothing could lead directly to him.
But once police became involved, that routine changed - and he left a clue that led them to him.
On the morning of July 11, Grant Misell's medical notes - taken by Chua, the nurse on duty - showed no cause for concern.
But in reality the 41-year-old was in terrible pain, and slipping into a coma.
Chua, the records show, did nothing, and alerted no-one. And yet a routine blood sample he took - expecting it to be routinely destroyed - was the proof of what he had done.
The police investigation meant it was kept for analysis, and that analysis revealed a dangerously low sugar level in Mr Misell's blood - along with traces of the factory-made insulin which had caused it.
Chua was arrested in January 2012, but it would be more than two years before the final charges were laid against him. He denied everything.
The case prosecutors made against him at Manchester Crown Court was long and laborious.
- How the sudden illnesses of patients under his care could have no natural cause.
- How the timings of those sudden illnesses matched the pattern of his shifts.
- How he had access to the medical supplies that caused them and the treatment rooms where they were administered.
Detective Superintendent Barraclough described the case against him as `a giant jigsaw puzzle' - where none of the pieces, on their own, seemed like anything - but put together, made a complete picture of his crimes.
Nobody was ever able to explain his motive.
In court - at least in the presence of the jury - Chua was mild and self-effacing.
His neighbours on the terraced street in Stockport where he lived refused to believe anything bad of him. And prosecutors never suggested any possible reason why he would harm the very patients he was supposed to help.
And yet a jury found that he did. Now he faces years behind bars. It is possible that we will never know the reason why.