In a document entitled "Responsibility for the terrorist atrocities in the United States," posted on the web site of the British Prime Minister, Tony Blair, there is the following statement:

14. Since 1996, when the Taleban captured Kabul, the United States government has consistently raised with them a whole range of issues, including humanitarian aid and terrorism. Well before 11 September 2001 they [the United States Government] had provided evidence to the Taleban of the responsibility of Al Qaida for the terrorist attacks in East Africa. [Emphasis added.] This evidence had been provided to senior leaders of the Taleban at their request.

Until I read this, I was unaware that the United States had already furnished, to the Taliban, evidence that Osama bin Laden and Al-Qaida were responsible for terrorist attacks.
The report continues:

18. Despite the evidence provided by the US of the responsibility of Usama Bin Laden and Al Qaida for the 1998 East Africa bombings, despite the accurately perceived threats of further atrocities, and despite the demands of the United Nations, the Taleban régime responded by saying no evidence existed against Usama Bin Laden, and that neither he nor his network would be expelled. [Emphasis added.]

Therefore, it would seem that the demand of the Taliban for evidence against bin Laden is specious, and is nothing more than a delaying tactic.