Nah he didn't right "that letter"
The former FBI director has asserted his belief that Osama Bin Laden died in 2002 of Kidney disease and Marfan Syndrome induced complications. The letter in question mentions the 2008 financial crisis which Bin Laden was not around to see. This letter was written by another Taliban member or more than one.
Osama Bin Ladens 2011 death was a known hoax.