In Pictures: 20 images that documented the horror of 9/11

Thick smoke billows into the sky (Daniel Hulshizer/AP)

September 11 was a day of indelible images — apocalyptic, surreal, violent, ghostly, both monumental and profoundly personal. Wrenching to remember. Impossible to forget.

The terrorist attacks in the US were captured in countless pictures by news photographers, bystanders, emergency service personnel, security cameras, FBI agents and others. Even an astronaut on the International Space Station took some.