'Arrogant, cunning and dangerous' criminal without remorse

He injected his victims with insulin, which is quickly undetectable, on wards at Leeds General Infirmary and St James's Hospital over a seven-month period in 2002.

With easy access to drug cupboard keys, he was able to give lethal injections to four vulnerable patients. Senior detectives branded him "arrogant, cunning and dangerous".

His crimes were only uncovered when a doctor sent blood for analysis following the nurse's attack on his fifth and last victim, 86-year-old Ethel Hall, amid surprise she had slipped into a hypoglycaemic coma despite not being diabetic. Her insulin levels were 12 times the norm and she died three weeks later.

The West Yorkshire Police investigation was complicated by the fact officers were already investigating another rogue nurse on the same ward at the infirmary. Emma Webster was later convicted of stealing painkilling opiates to feed her own addiction. Officers believe Norris, who was sometimes a counter-signatory when Webster accessed the drugs, saw how she evaded discovery and decided to use insulin to kill his victims.

He was convicted of the attempted murder of Vera Wilby, 90; the murder of Doris Ludlam, 80; the murder of Bridget Bourke, 88; the murder of Irene Crookes on her 79th birthday; and the murder of Mrs Hall. All were being treated for hip fractures and died after suffering brain damage due to the hypoglycaemic attacks which are rare in non-diabetics.

By the time he attacked Mrs Hall, he was so confident he predicted to colleagues the time she would collapse. He said he had a "funny feeling" and predicted she would "go off" – suffer some sort of collapse. It would be "just his luck" as he would have all the paperwork to do if she died, complaining to a colleague that whenever he did nights someone always died and it was always "about 5.15am".

When she fell into a coma he pointed to his watch and callously told her: "I told you so.""

West Yorkshire Police built up their case by taking 7,000 statements from staff, relatives and patients and seizing 3,000 exhibits.

It remains unlikely a motive will ever be established. Officers said Norris has never shown the slightest degree of remorse.

Glasgow-born Norris, now 33, formerly of Kirkstall, Leeds, is serving his sentence in Frankland Prison, Durham, where inmates nicknamed him "Dr Death".

Hospital chiefs have already admitted inadequacies and have paid out compensation of 47,500 to one bereaved family hit by Norris's crimes. Other cases are pending.