Greater Manchester Police said the investigation into the deaths at Stepping Hill Hospital in Stockport remains open, the Manchester Evening News reported. Assistant Chief Constable Terry Sweeney called the case "one of the most complex our detectives have ever worked on."
When Rebecca Leighton, 27, was arrested in July, police charged she used contaminated saline solution to kill at least two patients. Investigators said they were looking into at least seven deaths at the hospital.
Leighton released a statement thanking her family, friends, legal team and the staff at Styal Prison in Cheshire, the BBC said. She said her life had been "turned upside down."
"I have been living in hell and was locked up in prison for something I had not done," she said.