Four prison officers charged over the death of an inmate have been cleared.
Daniel Daymond and Samantha Prime were cleared of manslaughter
Michael Bailey, 23, from Birmingham, was found dead at Rye Hill prison on the border of Warwickshire and Northamptonshire in March 2005.
Daniel Daymond, 23, and Samantha Prime, 29, both of Rugby, and Paul Smith, 39, from Warrington, were cleared of manslaughter by gross negligence.
Ben King, 21, from Daventry, and Mr Daymond, were also cleared of perverting the course of justice.
Drug dealer Michael Bailey was found hanged by his shoelace while in the segregation block at the privately-run prison.
The prison had previously been criticised by Government inspectors for having too few, and often inexperienced, guards controlling inmates.
Clearing the defendants of all charges, Mr Justice Grigson told Northampton Crown Court that failures in the prison system may have contributed to the death of Mr Bailey.
"I am not saying that there is no fault or failing in the system or of any individual - my judgment relates solely to these defendants," he said.
"I recognise that this decision may add to the distress of Mr Bailey's family. That I deeply regret, but I cannot avoid my responsibility."
Speaking after the hearing, the defendants criticised staffing levels and management of the prison.
Too few staff were left with too many jobs to carry out and managers failed to act on concerns, they said.
Michael Bailey was found dead in his cell at Rye Hill prison
Mr Daymond's solicitor, David Leigh, said officers on the segregation unit had to complete an "impossible" 30 different tasks each day.
"It is plain that there are, or were, serious failings," he said.
"It's apparent from the evidence that quite a number of officers had no experience, not just on the segregation unit but in the prison generally."
As she left court, Mr Bailey's mother, Caroline, said she was left "angry and disappointed" by the judge's ruling.
"Individuals have failed in their duty of care and it is something that could have been avoided," she said.
"I hope the outcome of this case brings changes."