Pakistani born Abid Naseer has pleaded not guilty to terrorism charges in a New York court.
The 26-year-old who was extradited from Britain along with several others is accused of taking part in an international al Qaeda plot to attack targets in the United States and Europe.
Naseer is facing up to life in prison on charges including providing material support to al Qaeda and conspiring to use a weapon of mass destruction against the English city of Manchester.
His court appointed lawyer says much of the evidence against his client is circumstantial.
However Naseer is also accused of involvement in the 2009 plot to bomb the New York subway system. Two other alleged conspirators have already pleaded guilty to planning the attacks and a third was found guilty last year.