Michael Ledeen's sources within Iran told him that Osama bin Laden died of kidney failure while in Iran this past December. He is said to have spent most of his time there since the fall of the Taliban government in Afghanistan.
Cited as proof: for the first time, al-Q's happy hajj message was given not by Osama bin Laden, but by Ayman Zawahiri.
Source: Michael Ledeen writing at the National Review Online.
Hat tip: Rantburg