The families of the 96 people killed in the Hillsborough tragedy will be able to see thousands of unpublished documents relating to the disaster for the first time.
The Hillsborough Independent Panel has been overseeing the release of papers from around 80 organisations including the government, police, emergency services, Sheffield City Council and the South Yorkshire coroner.
Many of the families of the 96 people killed at Hillsborough believe that there was some kind of cover up on an establishment level to blame the fans for Britain's deadliest sporting disaster.
A memorial to the 96 outside Liverpool's Anfield Stadium
Liverpool fans scrambling to escape the crush in 1989
A report into the disaster by Lord Justice Taylor, published in 1990, found that the main reason for the disaster was a failure of "police control" but the Crown Prosecution Service decided there was insufficient evidence to bring a prosecution.
The victims' families say it is an injustice that no individual or organisation has been held fully accountable for the disaster.
They believe a major incident plan was never initiated by South Yorkshire Police and fans in the Leppings Lane end were denied emergency medical attention.
The 96 Liverpool supporters died in a crush at Sheffield Wednesday's Hillsborough stadium on April 15 1989 where their team were to meet Nottingham Forest in an FA Cup semi-final.
The families also dispute the findings of an inquest into the deaths, which ruled that the victims were all dead, or brain dead, by 3.15pm and which subsequently recorded a verdict of accidental death.
The 400,000 pages will be released to the families first.
People in Liverpool will observe two minutes of silence as a mark of respect for the 96 victims.
The city will also stage a vigil to show support for the victims' families following the disclosure of the Hillsborough documents.
The city's executive mayor, Joe Anderson, said: "With the release of these documents, we are hoping to get the truth of what happened more than 23 years ago.
"The importance of this day cannot be underestimated, as it will trigger the start of a process which will lead to justice for everyone affected by the tragedy."
The two-minute silence will take place at 3.06pm - the time the FA Cup semi-final was abandoned - as the bells at Liverpool Town Hall and other civic buildings ring out 96 times.
Flags at council properties will be flown at half mast throughout the day.
A report explaining the contents of the documents will be published by the panel, chaired by the Bishop of Liverpool, the Rt Rev James Jones.
Liverpool supporters hold up a flag in memory of the 96 who died in Britain's deadliest sporting disaster
Later, Prime Minister David Cameron will address MPs in the House of Commons and the documents will be uploaded to a website for viewing by the general public.
Margaret Aspinall, chairwoman of the Hillsborough Families Support Group, said they hope the documents will answer some of the questions they have about the causes and aftermath of the tragedy. "This is what the families and the fans have been fighting for 23 years.
"Without the truth you cannot grieve and where there is deceit, you get no justice," Mrs Aspinall, 65, said.
The families will see the documents at Liverpool Cathedral and are being advised by two of Britain's best known lawyers, Michael Mansfield QC and Lord Falconer.
It is expected the families will meet in the coming days to decide what action to take, if any, following the disclosures.
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