According to files recently received by George Washington University's National Security Archive, the U.S. has been pushing Pakistan since the early and mid 1990's to close down its terrorist safe havens, and documents times and places where Pakistani troops trained and/or fought with Taliban or terrorist leaders. Of course this was before 9/11.
Here is the portal page. The actual documents are available here, heavily redacted, in pdf format. There are also short summaries of the docs provided by GWU.
I’m not writing more because I have to read them, first.