LONDON: A medical mystery that began four years ago with unexplained deaths in a British hospital ended on Monday when a nurse was convicted of using insulin to murder two patients.

The 49-year-old nurse was also convicted of trying to poison 20 other patients during what police called a reign of terror at Stepping Hill Hospital in Stockport, 200 miles northwest of London.

In a note found by police, Victorino Chua described himself as “an angel turned into an evil person”.

The father of two wrote “there’s a devil in me” and that there were certain things he would “take to the grave”. Prosecutors said he took his frustrations out on his patients. Chua was found to have injected insulin into saline bags and ampules.

Other nurses who were not aware of the tampering then used the bags and ampules, leading to insulin overdoses. The nurse was cleared of a third murder charge but convicted of attempting to cause grievous bodily harm to that patient. Other patients recovered after receiving similar insulin overdoses.

Hospital officials first contacted police in July 2011 after finding contaminated vials of saline and “unexplained” low blood sugar levels in some patients. After finding the vials contained high levels of insulin, police launched a formal investigation.

Prosecutors first charged another nurse, 27-year-old Rebecca Leighton, with a variety of crimes but the case against her was dropped due to insufficient evidence.

Chua was not charged with the murders and poisonings until March, 2014.

Manchester Police Chief Peter Fahy on Monday apologised to Leighton for the time she spent in jail after she was charged.

He said Chua seemed unfazed by her imprisonment: “He was quite happy to stand by while she suffered the consequences.”

One of Chua’s victims was a 44-year-old multiple sclerosis patient being treated for a mild chest infection, who was pronounced dead eight hours later after being treated with a saline ampule containing large amounts of insulin. The other was an elderly man also with a chest infection, who was put on a saline drip contaminated with insulin. He died 10 days later.

Published in Dawn, May 19th, 2015

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