Isi-Meeting In Washington

From 9/11 Encyclopedia:

General Mahmoud Ahmad of the Isi, was in Washington for one week from September 6th- September 15th, 2001. 

Ahmad had in fact arrived in the U.S. on the 4th of September, a full week before the attacks.
The purpose of his meeting at the State Department on the 13th was only made public "after" the September 11 terrorist attacks, when the Bush Administration took the decision to formally seek the "cooperation" of Pakistan in its "campaign against international terrorism." Ahmad had two meetings with Deputy Secretary of State Richard Armitage, respectively on the 12th and 13th. 

After September 11, he met Senator Joseph Biden, chairman of the Committee on Foreign Relations of the Senate.
Confirmed by several press reports, he had "a regular visit of consultations" with U.S. officials during the week prior to September 11, 
--i.e. meetings with his U.S. counterparts at the CIA and the Pentagon. 
This included US Under Secretary of State for Political Affairs, Marc Grossman. 

During Ahmads visit, on the 9th of September, the leader of the Northern Alliance Commander Ahmad Shah Masood was assassinated.
The reason for Ahmads' visit wasn't made public. Later even his name was altered (changed into "inaudible") in a trabscript on questions during a Pentagon-press conference. (See Ahmad, General Mahmud)

Only 1 day before September 11th, Paknews speculated, that "one can safely guess that the discussions must have centred around Afghanistan,
relations with India and China, disarmament of civilian outfits, country's nuclear and missiles programme and, of course, Osama Bin Laden."