Mr Osborne, of the Kent and Essex Serious Crime Directorate, said the case was investigated with a view to bringing a manslaughter charge against the nurse and a corporate manslaughter charge against the hospital, but concluded that the death was a terrible mistake.
"I feel this is because of the pressure placed on nurses and junior doctors by the nurse in charge at the time, who was sister White, " she told the tribunal.
"As the nurse in charge Joanne should have ensured that the hospital policy was adhered to and clear instructions and supervision was given to the more junior nurse, " she said.