WASHINGTON - Accused September 11 criminal mastermind Khalid Sheikh Mohammed and four suspected co-conspirators were referred on Wednesday to trial before a Guantanamo war crimes tribunal on charges that could carry the death penalty, the Pentagon said.The five are charged with terrorism, hijacking aircraft, conspiracy, murder in violation of the law of war and other counts, and were referred to a capital military tribunal, meaning they could be sentenced to death if convicted, the Pentagon said.