One of the central allegations against Daily Telegraph owner Conrad Black - that he used company money to buy historical documents related to the former United States president Franklin D Roosevelt - yesterday became even messier. It emerged that Lord Black had been more extravagant with company money than previously believed; he spent $12m (£6.5m) acquiring the documents, not $8m.

He bought the photos, memos, letters and other artefacts while researching a book he was writing on the life of the former president, which was published in November. He defended the purchases when they were reported in August, comparing them to corporate art buying.

It was unclear last night how the extra cash was uncovered. But the special committee examining the financial affairs of the newspaper firm, Hollinger International, is looking closely at the use of company money, issues of disclosure and the role the board played - if any - in approving the purchases.

Hollinger is working to cut back the lavish lifestyle Lord Black enjoyed. It is selling the Roosevelt papers, has grounded two corporate jets and closed the tycoon's tab at the fashionable New York restaurant, Le Cirque. Interim chief executive Gordon Paris is leading the special investigating committee.