9 11
The terrorist attack that destroyed the World Trade Center on 11 September 2001 became known as 9/11. (PROSE: I Was a Monster!!!, The Danger Men)
The Laughing Gnome sent William Bishop's soul from 2011 into Calum Bence's body in 1999. Bishop had to overcome the urge to warn the authorities about 9/11. There were budget cuts to secret service espionage in 1999, but Bishop knew that changed after 9/11. (PROSE: The Danger Men)
In 2002, the Capricorn Killer wrote in his diary: " I want - no, I need - to be 9/11 not Big Brother."
Mark Whitaker was a man from 2011 sent back in time to 1994 by the Weeping Angels. In 2003, he said to the Eleventh Doctor: (PROSE: Touched by an Angel)
All the good people who have died, where I've stood by and done nothing. How do you think I felt on September the 11th, watching all those people die? But I did nothing.
In 2005, Emily Chaudhry and Francis Currie remembered the 11 September attacks; the media wondered if the attacks were due to British involvement in Iraq. (AUDIO: The Longest Night)