See these entries in Paul Thompson's book The Terror Timeline:
(Osama in the care of Pakistan's military...)
"September 10,2001: Pakistan Guards Osama as He Receives Medical Treatment
CBS later reports that on this day, bin Laden is admitted to a military hospital in Rawalpindi, Pakistan, for kidney dialysis treatment. Pakistani military forces guard bin Laden. They also move out all the regular staff in the urology department and send in a secret team to replace them. It is not known how long he stays there. [CBS News, 01/28/02]" (pg. 253)
(While Pakistan's military intelligence chief is in Washington...)
"September 4-11, 2001: ISI Director Visits Washington for "Mysterious" Meetings
ISI Director Mahmood visits Washington for the second time. On September 10, a Pakistani newspaper reports on his trip so far. It says his visit has "triggered speculation about the agenda of his mysterious meetings at the Pentagon and National Security Council" as well as meetings with CIA Director Tenet, unspecified officials at the White House and Pentagon, and his most important meeting" with Mark Grossman, U.S. Under Secretary of State for Political Affairs. The article suggests, "[O]f course, Osama bin Laden" could be the focus of some discussions. Prophetically, the article adds, "What added interest to this visit is the history of such visits. Last time [his] predecessor was [in Washington], the domestic [Pakistani] politics turned topsy-turvy within days." [The News, 9/10/01] This is a reference to the Musharraf coup just after an ISI Director's visit on October 12, 1992." (pg. 253)
Keep in mind Northern Alliance leader Ahmed Shah Massoud was assassinated in Afghanistan on September 9, possibly by al Qaeda operatives. Certainly bin Laden would have been a suspect when he checked into the Pakistani military hospital the next day. (He was already the prime suspect in the 1998 African embassy bombings.) Assuming that these press accounts are accurate and that bin Laden's kidney dialysis treatment took more than one day, why wasn't he arrested on September 11th or 12th? The Bush administration has called Pakistan an ally in the "War on Terror", which would suggest that Pakistan's military intelligence chief would have provided the information necessary for the US to immediately capture bin Laden. Also, Pakistan's ISI was practically built by the CIA and most likely continues to receive substantial funding from the US government, so it seems implausible that the ISI Director would have not told, at the very least, CIA Director Tenet where bin Laden was.