The story of the SLA gripped the nation. Now a film captures the craziness of the times. Robert Stone was editing his documentary about the Symbionese Liberation Army, the 1970s revolutionary group, when, only blocks away, a far more dangerous organization unleashed the most devastating attack ever on U.S. soil. “I was right there,” Stone recalls of working in Lower Manhattan’s Tribeca district on Sept. 11, 2001. As one of the first people to get out of the neighborhood, the filmmaker himself was surrounded, at one point, by dozens of news cameras. “Not only was I in the middle of