nicolette williams as worked as a park ranger at the national mall in washington, d.c. years. she enjoys interacting with tourists from all over the globe. >> every single day, we work at our different memorials and provide historical tours at those memorials for the visitors. >> on august 23rd, 2011, she's assigned to the washington monument. >> it's 500 feet up and we have windows on all four sides. you can see very far into maryland, virginia, about 30, 35 miles at least. >> security camera footage from just before 2:00 p.m. shows nicolette on the observation level as high up in the monument as visitors can go. she's waiting to take a group of about 20 tourists down in the elevator. >> as i'm sitting there, the elevator actually starts to make noise. >> she realizes immediately something unusual is happening. >> i know the elevator's noises and these are loud banging sounds, then the walls of the elevator begin to vibrate. >> the monument begins to shake dramatically. nicolette doesn't know what is happening, but she knows staying on the observation level is probably