U.S. military tribunals convene on Wednesday in the war crimes trials of two Guantanamo prisoners, a Yemeni accused of guarding Osama bin Laden and a Canadian captured in Afghanistan when he was just 15 and charged with murdering an Army medic. The hearings will convene on the fourth anniversary of the arrival of the first prisoners at Guantanamo and represent the latest attempt by the Pentagon to move forward with the trials, which have been repeatedly blocked by legal challenges. Full Story