US President Barack Obama said Americans would carry on despite continued threats against their safety.
In the 10 years since 9/11 attacks, the US has arrested nearly 3,000 on terrorism charges and convicted over 2,500.
US Defence Secretary Leon Panetta said the plane hijackers underestimated the country.
Day in Pics: 20th December
Showbiz World - December 20, 2014
People Magazine Awards 2014