Norris, 32, of Egilsay Terrace, Glasgow, killed the vulnerable women by giving them massive doses of insulin when they went into hospital in Leeds in 2002.

He was given four life sentences with a minimum term of 30 years for each of the murders and a 20-year sentence to run concurrently for attempted murder.

Jailing him at Newcastle Crown Court, Mr Justice Griffith Williams said: "You are, I have absolutely no doubt, a thoroughly evil and dangerous man... arrogant and manipulative, with a real dislike of elderly patients.

"There cannot be any suggestion you were motivated to hasten their ends to spare them suffering; indeed, there was no evidence that any of them was suffering apart from the pains that the elderly sometimes have.

"I suspect you enjoyed the power that ending a life gave you, choosing the elderly because they were defenceless.

"Then, emboldened by the fact that nobody suspected what was happening, it is clear you embarked on what in truth was a campaign of killing - a campaign which would, no doubt, have continued had not experienced medical staff been alerted to what was happening."

The judge said he had considered imposing a full life sentence without any early release.

The aggravating factors were that the victims were vulnerable, Norris breached the trust others had in him as a nurse and that there was a degree of premeditation.

Norris showed no emotion as he was led away from the dock.

West Yorkshire Police detectives have said he showed no remorse for killing Doris Ludlam, 80, Bridget Bourke, 88, Irene Crookes, 79, and Ethel Hall, 86, while he worked at the Leeds General Infirmary (LGI) and the city's St James' Hospital.

He also tried to kill Vera Wilby, 90, but she survived the coma which followed the unnecessary insulin injection.

Police began an investigation after Dr Emma Ward noticed in November 2002 that Mrs Hall had slipped into a hypoglycaemic coma despite not being a diabetic.

Detectives looked at other deaths on the wards from comas when Norris was working and after a lengthy investigation found that by the time Dr Ward raised her concerns he had already killed three times and failed with another attempt.

The nearest the prosecution came to outlining a motive was to suggest that Norris disliked working with the elderly.

All his victims were frail after suffering from hip problems, and could all have been considered a burden to nursing staff.