Audio has been released, supposedly of Osama bin Laden, in which he threatens to kill Americans if the U.S. executes the mastermind of the 9/11 attacks. Khalid Sheikh Mohammed is one of five terror suspects due to be tried in New York for the 2001 atrocities. The men involved could face the death penalty if found guilty of war crimes and murder. But a U.S. counterterrorism official dismissed the threat to execute any Americans captured by al-Qaeda. Some U.S sceptics believe Bin Laden died years ago, rendering all recent broadcasts by him as fakes.