A "thrill-seeking" nurse who murdered two patients and harmed 15 more is the only one to blame for his actions, an independent inquiry has ruled.
Geen was sentenced to a minimum of 30 years
Benjamin Geen, 25, of Banbury, was given 17 life sentences in May after he injected patients with lethal drugs.
A health authority review into the circumstances surrounding the attacks has ruled that no-one but Geen himself was responsible for what took place.
The offences happened at Oxfordshire's Horton Hospital between 2003 and 2004.
At his trial, Oxford Crown Court heard how the staff nurse injected patients with drugs such as muscle relaxants, insulin and sedatives to stop their breathing.
He then precipitated dramatic emergency ward scenes to satisfy his lust for excitement, the court was told.
Anthony Bateman, 66, from Banbury, died on 6 January, 2004 and David Onley, 77, from Deddington, died on 21 January, 2004 .
Fifteen other patients recovered shortly after they developed breathing difficulties.
Geen was told he must serve at least 30 years after he was found guilty of two counts of murder and 15 of grievous bodily harm.
The seven-month independent report was commissioned by the Strategic Health Authority (SHA) to "identify what lessons can be learned across the wider NHS" to reduce the risks of a similar incident happening.
In the review, Dr Simon Tanner, regional director of public health for the NHS South Central, said: "The report shows that no system or individual, other than Benjamin Geen himself, was to blame for the harm inflicted on those patients involved.
"The report acknowledges the prompt actions of staff within the A&E department at the Horton Hospital for identifying Benjamin Geen's actions early enough so as to prevent any further harm being done to other patients."
He said there is "no way" the NHS can prevent such an incident from occurring again - the risks can only be "minimalised".
"People join the NHS to help patients; it is therefore difficult for other staff within the NHS to understand the terrible actions of Benjamin Geen," he said.
The report recommended that a "robust" process should be set up for managing any similar investigations in the future and ensure all suspicious incidents can be easily tracked.
Trevor Campbell Davis, chief executive of the Oxford Radcliffe Hospitals NHS Trust, which includes the Horton, said it was considering "in detail" the practical suggestions and would take "any appropriate actions".