Poison probe focuses on seven cases
Police believe four more people were poisoned by contaminated saline at Stepping Hill Hospital.
Following the release of nurse Rebecca Leighton, Greater Manchester Police said they are looking at around 40 potential victims who may have been harmed by the contaminated saline.
It is understood they now believe that seven within that pool were poisoned - including Tracey Arden, 44, Arnold Lancaster, 71, and Alfred Derek Weaver, 83.
Fifteen of those potential victims have been eliminated from the inquiry, while the cases of 20 others are still being assessed.
Sources confirmed that a "Cracker"-style criminal profiler was brought in by police to help identify the mystery poisoner.
The forensic clinical psychologist, who has assisted various police forces in several recent high-profile murder cases, was called in at the beginning of the major inquiry into who sabotaged saline at the Stockport hospital.
He is not currently part of the investigation but initially aided detectives in drawing up the likely background of the saboteur.
A police source said: "He was brought in at the early stages of the investigation and helped draw up a profile of the perpetrator. He is currently not helping with our inquiries."
The source did not disclose how useful that information was or whether it played any role in the detention of Miss Leighton.
The 27-year-old spent more than six weeks in custody but was dramatically freed on September 2 after proceedings against her were discontinued due to insufficient evidence.