NEW scientific evidence casts fresh doubt on the conviction of a nurse jailed for a minimum of 30 years for murdering four women and attempting to kill another, according a TV investigation.

Glasgow-born Colin Norris was jailed for life in March 2008 after he was found guilty of murdering Doris Ludlam, 80, of Pudsey; Ethel Hall, 86, of Calverley; and Bridget Bourke, 88, and Irene Crookes, 79, both of Leeds – and the attempted murder of 90-year-old Vera Wilby, of Rawdon, while he worked at Leeds General Infirmary and St James’s Hospital, Leeds, in 2002.

A jury at Newcastle Crown Court was told that Mrs Hall, who was not diabetic, had been injected with a massive and fatal dose of insulin.

Tests showed insulin levels 12 times the norm, the court heard.

Norris has always protested his innocence and denied injecting patients with insulin. His case is under review by the Criminal Cases Review Commission.

A BBC Scotland investigation has now raised the possibility that all of Norris’s victims could have died from natural causes.

In a programme screened on Tuesday night – The Innocent Serial Killer? – two experts question the validity of tests results.

The BBC said it is making its evidence available to the CCRC.