British prosecutors today dropped charges today against the 27-year-old nurse accused of poisoning patients at a hospital.
It is "no longer appropriate" to continue the case against Rebecca Leighton, who was charged with contaminating saline drips at Stepping Hill Hospital, Stockport, the Crown Prosecution Service said.
Crown Service prosecutor Nazir Afzal said: "The inquiries, which are still ongoing, have not so far provided us with a stronger case which would meet the test that there is sufficient evidence for a realistic prospect of conviction."
Ms Leighton, who was arrested in July by detectives investigating the deaths of patients, was being freed from jail this afternoon.
The CPS said Greater Manchester Police's investigation into the deaths continues and "if further evidence is presented", then the prosecution could be re-started.
Mr Afzal added: "Rebecca Leighton was charged on the basis that there was a reasonable suspicion she had committed the offences and there were reasonable grounds for believing the continuing investigation would provide further evidence within a reasonable amount of time.
"When we make a decision on this basis, it would be wrong of us to keep a suspect in custody indefinitely without keeping a very close eye on what evidence is emerging and whether objections to bail can be justified."
Ms Leighton was held in Styal Prison while a trial date was being set for next year amid accusations that she tampered with saline ampoules, saline bags and medical products.
Mr Afzal said: "We have conducted a review of the case with senior police officers and sought the advice of leading counsel on whether it would be right to keep Rebecca Leighton in custody while investigations are continuing.
"The advice we have received is that on the evidence currently available there is not a case in law which could proceed and that the charges should be discontinued.
"We have therefore this afternoon informed the prison where Rebecca Leighton is being held on remand that the case against her has been discontinued and she can be released immediately. It is right and proper for us to do this.
"As this is very much a complex investigation with lines of inquiry still being followed, there is the prospect that further evidence might emerge which the CPS would then consider alongside the evidence gathered so far. The law does allow us to reinstate charges in those circumstances, particularly where the allegations are serious."
Mr Afzal said there was "sufficient evidence" for a conviction against Ms Leighton over one charge of theft of medication but "we have decided it is not in the public interest to proceed" considering the time she had already spent in custody.
Police continue to investigate the suspicious deaths of Tracey Arden, 44, Arnold Lancaster, 71, Derek Weaver, 83, and Vera Pearson, 84.
The alarm was raised when a higher than normal number of patients were reported to have "unexplained" low blood sugar levels.