Geoff Craighead (July 15, 2009). "Daredevils, Protestors and Suicides". High-Rise Security and Fire Life Safety. Butterworth-Heinemann. p. 116. ISBN9780080877853. Retrieved February 4, 2014. Quoting from: Gillespie, Angus K. "Twin Towers: the Life of New York City's World Trade Center." Rutgers University Press, 1999