Loved ones of those killed in the 2001 terror attacks took to a podium to voice their concerns, and scores more huddled under umbrellas and braved the cold.
"We're here not just to send a message to New Yorkers but to the people of America to become energized and activated," said Debra Burlingame, 55, whose brother, Charles, was the pilot of American Airlines flight 77, which crashed into the Pentagon. "My brother spent the last minutes of his life fighting highjackers, he would want me to fight against the trial. "
Khalid Sheikh Mohammed and four other 9/11 suspects are due to be tried in New York's federal court after being transferred from Guantanamo Bay, Cuba. The courthouse is just a few blocks from the World Trade Center site.
"I don't think they should put the city at risk of another attack," said Dennis O'Berg, 62, from Dyker Heights, Brooklyn. His firefighter son, also named Dennis, died in the twin towers