Detectives probing the deaths of mental health patients across Essex are looking into 25 cases at nine mental health units.
Police were already investigating the deaths of seven people in the care of North Essex Partnership NHS Foundation Trust after Matthew Leahy, from South Woodham Ferrers, died at the Linden Centre, in Chelmsford, in November 2012.
An inquest into the 20-year-old’s death found there had been “multiple failings” at the centre.
Matthew’s mum, Melanie, 52, from Tolleshunt Knights, said police are looking at bringing corporate manslaughter charges.
She said: “There have been so many safety issues over the years. They are now looking not just at the Linden Centre but at all the establishments run by the trust, because they have been using the same staff and moving them from A to B.”
In Matthew’s case, an inquest heard observation slots were missed, the ward was short-staffed and no care plan was put in place after he was sectioned a week before his death.
Three nurses were disciplined after they admitted later falsifying records but Mrs Leahy was told last month police will not be pressing charges.
Two years ago a Care Quality Commission (CQC) report found the trust required improvement and warned bosses there were still too many places where patients could hang themselves.
The police announcement came during the inquest of another Linden Centre inpatient, Patrick Aspbury, 23, who was killed by a train at Chelmsford railway station. His death is understood not to form part of the enquiry.
The trust has now merged with the South Essex Partnership University NHS Foundation Trust, to form the Essex Partnership University NHS Foundation Trust.
As a result, it now runs mental health services in south Essex but it is unclear exactly where the investigation will focus.
The trust previously ran mental health services in Colchester, Chelmsford, Harlow, Clacton, Braintree, Witham and Epping, as well as primary care services in Thurrock and Grays.
Mrs Leahy said: “I think the shout needs to go out to the areas where the trust was caring for people. Also, the police are going back to 2000 but families are contacting me going back to 1995.”
Sofia Dimoglou, whose 76-year-old mother Valerie Dimoglou killed herself while on day release from The Lakes, in Colchester, told Channel 5 news her mother said she would kill herself if she was made to leave hospital.
She said: “There was quite a lot of shrugging of shoulders and the main point was she can’t take a bed up any longer. She is not an emergency case.
“So there was really a lot of pressure, amounting to bullying at times, to get her out of hospital.”
Other deaths at the centre include Nicola Dordoy, 42, who died in 2001, Denise Gregory, 40, in 2004 and Ben Morris, 20, who hanged himself in 2008.
An inquest earlier this year found another Linden Centre patient, Richard Wade, died in May 2015 after he hanged himself with a dressing gown cord staff failed to take from him.
An Essex Police spokesman said: “In January 2017, Essex Police began enquiries into the circumstances of a number of deaths which have occurred involving patients in the care of the North Essex Partnership University Trust, including at the Linden Centre, since 2000.
“This work follows further allegations surrounding the death of Matthew Leahy at the facility in Chelmsford on November 15, 2012.
“The work has been led by the Kent and Essex Serious Crime Directorate. During the enquiry so far a number of people have been spoken to but no arrests have been made.
“Our investigation into this matter is continuing and we continue to keep the relatives of those involved updated at every stage.
“We are looking at nine establishments including the Linden Centre (so nine in total). We are investigating up to 25 deaths.”