A young Nigerian man pleaded guilty Wednesday to trying to kill nearly 300 people aboard a US-bound airliner on Christmas 2009 with explosives secreted in his underwear. "Do you understand that you have the right to remain silent?" asked judge Nancy Edmunds. "Yes," replied 25-year-old Umar Farouk Abdulmutallab. "Do I understand correctly that you wish to waive that right to plead guilty to all the charges in the indictment?" asked the judge. "Yes," again came the reply.