Campaigners representing hundreds of patients who died at Gosport War Memorial Hospital have accused Hampshire police of staging a cover-up that cost lives.
They criticised the initial investigation into the deaths, citing what they described as a "monumental conspiracy" to prevent the truth from coming out.
Speakers at a press conference included Bernard Page, 79, of Gosport, whose mother, Eva Page, died at the hospital in 1998.
Mr Page claimed that Hampshire Constabulary was preparing to issue a statement "relating to blatant criminality that has been covered up for some 26 years".
He said the statement would either admit that misconduct had been covered up to protect the force's reputation, or "perpetuate the denial of criminality" that had gone on for decades.
The deaths are now being probed by officers attached to the Kent-based Operation Magenta, the fourth police inquiry into what happened.
But relatives say they are not convinced the full facts will emerge.
Mr Page said: "It will become evident that that there has been a monumental conspiracy all along and that the scope of Operation Magenta has been contrived to ensure the criminality remains hidden."
READ MORE: Police probing hundreds of deaths at Gosport War Memorial Hospital have identified 24 suspects
Eva Page, who was suffering from cancer, died four days after being admitted to Gosport War Memorial Hospital.
Mr Page said his mother was given barbituates, adding that her death was not properly investigated. Had it been, he said, more deaths at the hospital would have been avoided.
The conference was chaired by David Wilson, of Sarisbury Green, whose 86-year-old aunt died in 2001.
He alleged that Hampshire Constabulary "dishonestly misled" health chiefs over the death of another patient, Gladys Richards, who was allegedly deprived of fluids.
Mr Wilson said the Crown Prosecution Service decided there was not enough evidence to prosecute anyone in connection with her death.
But he claimed the decision was influenced by what he described as the "dishonesty" of Hampshire police.
Mr Wilson added: "It is the duty of police to protect life.
"Hampshire Constabulary knew it should liaise with the Health and Safety Executive. There was a prima facie case for the successful prosecution under the Health and Safety Act, or the closure of the ward, which would have prevented further loss of life whilst a thorough and appropriate investigation was conducted."
After the press conference Hampshire police issued a statement that referred to the Independent Office for Police Conduct (IOPC).
It said: "Having considered a Right to Review request, the IOPC made a direction that we should provide a full rationale to the families in relation to complaints made.
"Our Professional Standards Department have since been conducting a full and thorough investigative review of the available documentation and decisions made, in order to provide a more full explanation to them.
"As part of this, we have been providing regular updates on our progress.
"While we were conducting this review, a man representing some of the families raised further issues with officers involved in completing this, which required further referral to the IOPC for their consideration and delaying the original matter.
"The IOPC ultimately dismissed these with no further action, at which stage we were able to fully resume the ongoing review.
"This work is ongoing and we will continue to provide updates to the family as we seek to provide them the full rationale."
In 2018 the Gosport Independent Panel published a report which said the quality of the first three police investigations into deaths at the hospital had been "consistently poor".
As reported at the time, Mr Wilson claimed that some officers had acted "corruptly", which Hampshire Constabulary denied.
Responding to his complaint, the force said: "There is a clear difference between an officer who has not done a job properly and an officer who is corrupt."
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