DETROIT, Michigan (AFP) - The so-called "underwear bomber" pleaded guilty Wednesday to trying to blow up a US-bound airliner on Christmas Day 2009, saying he had sought to avenge the killing of innocent Muslims. In a six-minute speech to a shocked courtroom on the second day of his high profile-trial in Detroit, Michigan, Umar Farouk Abdulmutallab insisted his actions were righteous and that the true crime was US foreign policy. "I am guilty of this count in US law but not in the Holy Quran," the 25-year-old Nigerian said as he confessed to trying to kill 289 people on a packed transatlantic airliner using explosives hidden in his underwear.