On September 11, 2001, “The 9/11 teams realised that their scheme might be compromised if team members were caught trying to smuggle illicit knives on board the planes and so carried box-cutter knives less than four inches long which were permitted by the Federal Aviation Authority. In addition to pepper sprays, these boxcutting knives were the only weapons carried by the hijackers.”
– Rohan Gunaratna, Inside al Qaeda, Pages 107-108