No further action will be taken against four doctors who held management positions at the Stafford Hospital during the height of care failings.
The General Medical Council says legal advisors said there was no realistic prospect of securing a finding against Dr John Gibson, Dr Valerie Suarez, Dr David Durrans and Dr Diarmuid Mulherin on the allegations made, so they had dropped the cases.
Niall Dickson, the GMC's chief executive, said he understood people felt "badly let down" over the fact very few people have been brought to book for failings in basic levels of care which were uncovered at the hospital, but he said: "The law is clear: we can only prosecute a doctor if there is sufficient evidence of that individual's wrongdoing."
Mr Dickson said the GMC only took the unusual step of publishing its legal advice because of the high level of public interest in Stafford Hospital.
Mr Dickson: "He (Tom Kark QC, leading counsel to the Francis Inquiry) advises us in the strongest terms that these cases cannot proceed to a hearing," said Mr Dickson.
"Mr Kark has told us that there is 'no realistic prospect' of securing a finding against these doctors on the allegations made.
"Following the extensive investigations we have undertaken - which Mr Kark acknowledges in his advice - there is not the evidence to establish either misconduct or impairment against any of the doctors.
"We know that many of those who saw and experienced the appalling care at the trust feel badly let down and frustrated that no-one is taking responsibility for what happened."
The GMC said to date it had investigated 44 doctors in relation to the Mid Staffordshire trust, concluding all but one of those cases - including the four investigations which have been ended today.
In 16 cases it was determined there would be no further action, while in 24 cases, doctors were given advice including two who were also warned.
Another doctor had "accepted undertakings" from the GMC, while another had also agreed undertakings and been issued with advice.
One doctor has been erased from the register.
In the letter outlining his decision, Mr Kark said: "Having reviewed all of the evidence which the GMC has now obtained from witnesses who were able to give direct evidence of the actions and omissions of these four doctors, we have advised that the evidence provides no sound basis for a finding of serious misconduct nor of deficient professional performance such as might lead to a finding of current impairment and accordingly in our view there is no realistic prospect of such a finding."
He added that the weight of the evidence gathered from witnesses was "favourable" to the doctors: "It provides a picture of well-intentioned individuals doing their best in difficult circumstances to improve poor standards."