Thousands of official documents relating to the 1989 Hillsborough football disaster, in which 96 Liverpool fans died, will be published for the first time in Britain on Wednesday.
The papers come from the files of 80 organisations including the British government, South Yorkshire Police, Sheffield City Council, the South Yorkshire coroner and the fire and ambulance services.
Government papers are not usually published in Britain until 30 years after they have been written, but lawmakers agreed to the full, uncensored disclosure of all papers relating to the 1989 tragedy in August last year.
The decision came after more than 100,000 people signed an online government petition to trigger a parliamentary debate on the issue.
The e-petition currently has more than 156,000 signatures.
Ninety-six Liverpool fans died after a crush on the terraces of Sheffield Wednesday's Hillsborough stadium during an FA Cup semi-final against Nottingham Forest in April 1989.
The families of those who died in Britain's deadliest sporting disaster were to have the first access to more than 400,000 pages of documents in Liverpool on Wednesday morning before they are disclosed to the public in the afternoon.
A report explaining the contents of the documents will be published by the Hillsborough Independent Panel, which has been overseeing the release.
A statement about the report will be made to lawmakers in the lower House of Commons later in the afternoon to which British Prime Minister David Cameron is expected to respond.
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 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 of the ground were denied emergency medical attention.