The death of a woman at Blackpool Victoria Hospital is being treated as a possible murder, police have said.
A post-mortem examination after the death of Valerie Kneale, 75, found an injury which police say is believed to be suspicious.
It follows an investigation into alleged mistreatment and neglect of patients at the hospital's stroke unit last November.
A police spokesman said no arrests had been made over Mrs Kneale's death.
In a statement, Ms Kneale's family said they were "completely and utterly devastated and heartbroken to have lost Val in these circumstances."
They added: "She was the most precious wife, mother and grandmother, our constant friend and problem-solver who we will miss dearly."
Blackpool Teaching Hospitals NHS Foundation Trust reassured patients that "all necessary actions to provide safe care will continue to be taken".
Police launched an investigation last year amid allegations that some patients had been poisoned on the stroke unit.
Three healthcare professionals were arrested and later released under investigation.
As part of the investigation, a number of post-mortem tests were conducted, including an examination of the death of Mrs Kneale.
This revealed an unexplained injury and, as a result, her death is being treated separately as a murder inquiry, said police.
A cause of death is yet to be established.
Det Ch Insp Jill Johnston, of Lancashire Police, said: "We understand this is a concerning development but I would like to reassure people we are fully committed to carrying out as thorough an investigation as possible.
"Specially trained officers are providing support to Mrs Kneale's family and my thoughts are with them at this difficult time."
Chief Executive of Blackpool Teaching Hospitals NHS Foundation Trust, Wendy Swift, said a "concern was raised" in November 2018 "regarding the care of patients on the stroke unit" and the trust responded "immediately" by contacting the police.
She added: "As part of the investigation a number of post-mortem investigations were conducted. During the course of one of these an unexplained injury was found to a 75-year-old woman. A cause of death is still to be established."
Ms Swift said the trust would like to reassure patients that "all necessary actions to provide safe care will continue to be taken and the provision of hospital services will be uninterrupted.''