A catalogue of failings allowed a nurse to murder four frail patients, according to a report.
Staff nurse Colin Norris gave the elderly women fatal doses of the diabetes drug insulin while they were being treated at two Leeds hospitals.
According to an NHS Yorkshire and the Humber independent inquiry report, problems including relatives' concerns going unheeded, staff knowledge of clinical governance policies and systems, record-keeping and medicines management, all contributed to the opportunities Norris had to get hold of drugs and murder patients.In 2008, a judge at Newcastle Crown Court handed Norris, from Glasgow, four life sentences for murdering Doris Ludlum, 80, Bridget Bourke, 88, Irene Crookes, 79, and Ethel Hall, 86, while he worked at Leeds General Infirmary (LGI) and the city's St James's Hospital in 2002.
A 20-year minimum sentence, to run concurrently, was imposed for the attempted murder of 90-year-old Vera Wilby, who survived a coma induced by an insulin injection.
The report, published on Tuesday, stated: "Colin Norris was a trained nurse who had access to drug cupboard keys and the means to administer lethal injections to elderly and vulnerable patients.
"There is evidence to suggest that the systems in place at the trust to monitor the supply and administration of drugs at the time of the incidents were not robust enough to identify and prevent malpractice."
It went on to say that actions taken by the consultant and medical director following the collapse of Ethel Hall in November 2002 were "prompt and effective", but if the earlier unexplained deaths of the other women had been reviewed and death certificates accurately completed, Norris's actions might have been spotted earlier.
In addition, problems with references when he was first employed and the merger of the United Leeds Teaching Hospitals Trust and St James' University Hospitals NHS Trust meant staff did not have a clear understanding of new systems.
Dr Peter Belfield, medical director of Leeds Teaching Hospitals, said "A determined killer like Colin Norris would be difficult to spot in any NHS organisation but I believe the systems we now have in place would make it much more likely to pick up on someone like this."