Why did a nurse turn to murder?

Norris killed patients at two hospitals in Leeds

Colin Norris told the jury at his trial that he became a nurse to "make a difference".

But instead of caring for his elderly and vulnerable patients, he killed them.

A jury has convicted him of four counts of murder and attempting to murder a fifth patient.

Glaswegian Norris applied to be a nurse, aged 22, and then trained at Dundee University.

So what caused him, while working at two Leeds hospitals four years later, to turn into a serial killer?

Psychologist Dr David Holmes, a senior lecturer at Manchester Metropolitan University, said he believed Norris was searching for a sense of power.

To think that one of our own has let us down so badly and somehow dented the trust we have with patients is very sad indeed Bobbie Chadwick, Royal College of Nursing

He said in cases where a nurse kills a patient there could also be a sense of competition with other professionals.

"This person may have felt that doctors rule the roost but 'I am as clever, I am the kind of person who can deal with life and death', and administers literally life and death to affirm their own status or self-appointed status," he said.

Dr Holmes said the deaths of elderly patients in hospitals were often expected, which is why Norris was not caught sooner.

He said: "We are dealing with patients who are falling into a category, as victims, that we call 'less than dead'. In other words, they are people that are not really being noticed very much compared with others.

Bobbie Chadwick said Norris was "one very sick rogue"

"They are not really that significant in terms of being really, really shocked at this person dying because it's kind of expected.

"So their deaths are less noticeable, as in the Harold Shipman case.

"These people can accumulate quite a few bodies before anyone becomes suspicious."

Bobbie Chadwick, deputy president of the Royal College of Nursing who works at Leeds General Infirmary, said Norris was "one very sick rogue" who had let the nursing profession down.

"I feel very sad, I feel very disappointed," she said.

"Nursing has achieved so much and we have such a good track record.

"It's inherent in every nurse to be a patient advocate, to protect patients, to safeguard their wellbeing and to think that one of our own has let us down so badly and somehow dented the trust we have with patients is very sad indeed."