For two decades, Ethel Hall's family believed that staff nurse Colin Norris murdered the 86-year-old by injecting her with insulin while she recovered from a broken hip in a Leeds hospital.
After his latest appeal against conviction, some members of Ethel's family are having doubts.
"The evidence, it's just not sitting right to me," daughter-in-law Helen Hall told a new BBC podcast, Disclosure Investigates: Killer on the Ward.
Norris was convicted in 2008 of killing Ethel and three other elderly patients as well as attempting to murder a fifth.
The Court of Appeal rejected his challenge against his convictions last year but the new BBC podcast has reviewed medical records, looked again at police interviews and heard about new scientific discoveries.
It reveals a scenario in which the murders may never have taken place at all.
The podcast series comes a week after a public inquiry reported on the case of former neonatal nurse Lucy Letby who was convicted of murdering seven babies and attempting to murder seven others at a hospital in Chester a decade ago.
While the circumstances are very different, Norris' supporters also argue that his case hinges on disputed interpretations of medical evidence.
The story begins in 2002 when Norris, a 26-year-old nurse, originally from Glasgow, found Ethel in an hypoglycemic coma as she recovered from a broken hip.
Doctors took blood samples to find out what caused her blood sugar to drop so low.
The test results seemed conclusive - she had a massive amount of insulin in her blood.
She died 21 days later, sparking a murder investigation.
A nurse who had been on shift on the night Ethel was found told the police that Norris had predicted the 86-year-old might not last the night.
He quickly became the prime suspect.
The police operation trawled retrospectively through all the deaths on Norris's wards, looking for potential murders that may have gone unnoticed.
They identified three other cases of unexplained severe hypoglycemic deaths and one where the patient recovered.
No blood tests had been taken from these cases at the time of their deaths to be able to prove insulin poisoning but experts for the prosecution said in court that their medical charts showed persistent and severe low blood sugar readings.
They said that because this was so rare in non-diabetics that it must be murder.
When it came to court in 2007, experts called by the defence said four of the five patients had died of natural causes.
But after a five-month trial and a deadlocked jury, Norris was convicted by a majority of 11-1 and told he would not be eligible for parole for 30 years.
After the verdict, Ethel's son Stuart Hall said: "I don't think he should come out again. He's got the knowledge to commit murder but do it discreetly."
When I got involved in the case in 2009, Norris, who is now known as Colin Campbell, had just lost his first appeal against conviction.
Two years later, new scientific evidence came to light which challenged one of the key assumptions underpinning the prosecution case.
It claimed hypoglycemia - low blood sugar - in the frail and elderly is not as vanishingly rare as was once thought, suggesting the jury had been misinformed.
This new evidence was submitted for a second appeal, which took another 14 years to be heard.
During that appeal last year, experts for Norris argued that the symptoms seen in several of the patients could occur naturally in elderly, frail people.
Experts for the Crown maintained the deaths were medically distinct.
They said their blood sugar readings were refractory, meaning they kept coming back despite being given glucose, whereas naturally-occurring hypoglycemia can be easily corrected with a treatment such as a sugary drink.
They argued this distinction could only be explained by deliberate insulin poisoning.
The ultimate question in this case has always been 'what happened to Ethel Hall?', the woman whose death sparked the investigation.
Was deliberate insulin poisoning the only explanation or could she have been given it accidentally?
Doctors who first attended Ethel suspected she'd been accidentally given insulin meant for another patient.
They looked to see if anyone in the neighbouring beds were due to be given insulin in the hours prior to this discovery.
But this mix-up theory was dismissed as no-one next to Ethel was due to receive it during the time frame under scrutiny.
However, as part of the BBC investigation, we found there had in fact been a diabetic patient elsewhere on the ward who was being given insulin in preparation for an operation around the time doctors were trying to save Ethel.
Ethel had been found in a coma at 05:00 and her first injection of glucose to increase her blood sugars was given at 06:15.
The syringe was administered by the ward doctor, who had asked Norris to prepare it for them.
Our review of witness statements and medical notes shows that immediately after this, Norris was preparing another 50ml syringe of dextrose to be injected via a cannula and a 500ml bag of dextrose for a drip.
At the same time, in the same treatment room, another nurse was arranging insulin mixed with saline in a 50ml syringe for the diabetic patient.
The nurse, who had gone to another ward to get the insulin, asked Norris to check the syringe dosage and apologised for not having the ampoule they had drawn it from.
Were the syringes accidentally switched?
Initially, we discounted this scenario because we assumed medical staff would be alerted if a diabetic patient had accidentally been given dextrose instead of insulin.
However, endocrinologist Prof Joel Zonszein, an expert in diabetes, said the amount given would not have caused a severe illness.
"The answer is very different from somebody getting insulin," he said.
"Insulin is much more aggressive. Giving too much sugar does not cause a coma and it will take more that 24 hours until the person goes into a coma. It's completely different."
Prof Zonszein also said the amount of insulin Ethel may have been given accidentally would have produced the high readings in her immunoassay blood test taken five hours later.
He said the drip of dextrose would have masked the insulin, making it harder to notice, but the blood test result would still register a very high level of insulin.
If the syringes were accidentally switched, is that a mix-up rather than a murder?
West Yorkshire Constabulary said its officers worked tirelessly to get justice for the victims and their families.
A statement from the police force said: "In June 2025, the Court of Appeal dismissed the appeals, with the judges saying they had no doubt about the safety of any of the five convictions."
But some members of Ethel's family said the result had not brought them the closure they'd hoped for.
Her son Stuart's wife Helen said: "I don't think it ever will [give us closure] until we know actually, one way or the other, whether he was guilty or not.
"If he's guilty, then fine, that's it.
"But if he's not guilty and he hasn't done it, the evidence that they're trying to keep him inside for, is not enough."
Ethel's family now believe the only thing that will give them peace of mind is a re-trial.
Helen Hall said: "I'm not saying that he should walk free. I'm not saying he should stay behind bars, he should have a fair trial."
Colin Norris's mother June said she will not stop seeking what she believes is justice for her son.
"If you're a mum, you know," she said.
"You'll fight for your kids till the very end."
