Insulin is a hormone produced by the pancreas to allow the uptake of glucose in the blood to be used by the muscles and cells of the body for energy.

At Stepping Hill it was suspected that, due to the increased levels of insulin in the patients' bloodstreams, they quickly became hypoglycemic and three confirmed fatalities occurred.

Meanwhile, several armed police guards were stationed at the hospital, and staff were made to work in pairs when administering medication to patients.

On 20 July 2011, GMP confirmed that they had arrested a 27-year-old nurse – Rebecca Jane Leighton, who worked at the hospital in wards A1 and A3 – in connection with the murder inquiry.

Forty-six-year-old Victorino Chua, a nurse at the hospital, had been arrested amid claims that forms had been altered and a patient given extra medication.

[14] By July 2012, GMP stated that they were making good progress in the investigation, that 22 people had been poisoned and that seven deaths had occurred.

[15] On 29 March 2014, Chua was charged with the murders of Tracey Arden, Arnold Lancaster and Alfred Derek Weaver, and 31 other offences including grievous bodily harm and attempted poisoning.

[17] He was found not guilty of murdering Arnold Lancaster, who had been suffering from terminal cancer, but was convicted of attempting to cause him and 20 other patients grievous bodily harm with intent by poisoning.

He was also found guilty of eight offences of unlawfully administering or causing to be taken by another person any poison or destructive or noxious thing with intent to injure, aggrieve or annoy, or attempt to do so, after deliberately altering prescriptions.