A hospital worker has been arrested on suspicion of murdering an elderly patient.
Detectives in Lancashire are quizzing a man over the alleged rape of two patients and a sex attack on another worker.
They said it follows a wider investigation into alleged mistreatment and neglect of patients at Blackpool Victoria Hospital's stroke unit, LancsLive reports.
They say their probe has been running since November 2018 and has involved a number of post-mortem examinations.
These included Valerie Kneale, 75, from Blackpool, who died from a haemorrhage caused by a non-medical related internal injury.
Following this, a separate murder investigation was launched.
Police said information relating to other allegations of serious sexual assaults against two patients were received, as well as the sexual assault of a healthcare professional working on the stroke unit.
A hospital worker was arrested on Wednesday on suspicion of murder, two offences of rape and one of sexual assault. He remains in custody for questioning.
He has also been suspended by Blackpool Teaching Hospitals NHS Trust.
The arrest is not linked to the ongoing investigation into allegations of poisoning and neglect.
Detective Chief Inspector Jill Johnston, of Lancashire Police, said they recognise the arrest and the nature of the allegations "will cause some alarm but want to reassure the public a major investigation is ongoing".
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She said: "We have today arrested a man in connection with a number of serious offences.
"We understand this will cause some significant concern in the community but please be reassured we have a dedicated team of officers conducting a number of enquiries.
"These are complicated and sensitive allegations which we are committed to investigating thoroughly.
"We are offering support to those involved and they are being updated throughout the process by trained officers.
"Our priority and the priority of Blackpool Teaching Hospitals NHS Foundation Trust is to ensure the safety of patients. We are working closely with the Trust as well as HM Coroner for Blackpool and Fylde as part of the investigation.
"If you have any information or have worked on the stroke unit and can assist with our enquiries, please come forward and speak to police immediately."
Anyone with information in connection with the investigation can contact police on 101 quoting log 0942 of March 3 or report it via the major incident portal here.
Alternatively, you can contact independent charity Crimestoppers on 0800 555 111 or online at crimestoppers-uk.org.
If you or somebody you know has been affected by this story, contact Victim Support for free, confidential advice on 0845 30 30 900 or visit their website, www.victimsupport.org.uk.