As the world marks the twelfth year since the September 11, 2001 terror attacks, a campaign called the ReThink911 Coalition is drawing attention to one of the lesser-known events of that day-the collapse of World Trade Center Building 7. Prior to the Sept. 11 attacks, 7 World Trade Center was a 47-story building just north of the Twin Towers. At 5:21 pm, nearly seven hours after the North Tower came down, 7 World Trade Center crumbled quickly to the ground. In 2006, Richard Gage, a San Francisco-based architect, founded Architects and Engineers for 9/11 Truth, which doubts Building 7 collapsed because of fire. Gage and other architects and engineers argue that 7 World Trade Center came down in a free fall, which could only have been caused by a deliberate demolition explosion. More than 2,000 architects and engineers have signed a petition calling for a new investigation into the building's collapse. [Architects and Engineers for 9/11 Truth] makes up large part of the ReThink911 coalition, which spent $44,000 to put [a 54-foot] billboard in Times Square at the heart of midtown Manhattan this week. The group says it raised $225,000 from more than 2,000 donors, the majority of whom gave contributions of less than $100. They're using the money to put up signs and billboards in seven American cities. They will be advertising in Vancouver, Toronto, London and Sydney too.