A police force involved in the initial investigation into the Hillsborough disaster has launched a trawl of its archives after finding documents relating to the tragedy at its headquarters.
West Midlands Police, which examined South Yorkshire Police's handling of the disaster, said the documents, some of which are understood to be held on computer disks, had recently been passed to the Independent Police Complaints Commission.
In a statement, the West Midlands force said "recent unrelated searches" of secure storage areas in Birmingham had "uncovered two items of material related to Hillsborough".
The statement added: "These documents have been passed to the IPCC to help in their investigation of the Hillsborough disaster.
"As a result of the find, West Midlands Police has announced a rigorous, systematic search of its archives which is expected to take around three months.
"Specially trained police search officers will scrutinise storage areas at Lloyd House, Nechells Green police station where the force's investigation of South Yorkshire Police was focused, and other buildings."
It is understood that the IPCC has yet to establish whether copies of the newly found documents were already held within material gathered by the Hillsborough Independent Panel, or in statements available to previous inquiries.
West Midlands Police's official archive storage facility in Derbyshire, where up to 17,000 documents are held, will also be subjected to further examination as part of the searches, which began last week.
West Midlands Police Deputy Chief Constable Dave Thompson said the force was committed to the IPCC's Hillsborough investigation and to supporting the new coroner's inquest due to be held next year.
The officer added: "We have no reason to believe West Midlands Police holds any more Hillsborough-related material but, due to the recent finds, we want to be able to assert this with the highest degree of confidence to the inquest coroner.
"That's why we've announced a rigorous, systematic search of all archived material in our buildings. This is a voluntary move initiated by West Midlands Police and demonstrates our commitment to openness and transparency.
"We will leave no stone left unturned. If any material relating to Hillsborough remains on West Midlands Police property, we are confident the search will uncover it."