Columbia 'puncture' theory examined
Nasa says the space shuttle Columbia's skin was almost certainly pierced, allowing superheated air to enter the left wing during descent.

Tears and tributes at Houston
The BBC's Nick Miles reports from the Johnson Space Center, where President Bush paid homage to the astronauts of Columbia.

Was Columbia struck by space debris?
Nasa officials are considering whether the fatal damage to Columbia's heat resistant tiles was caused by space debris while in orbit.

The Columbia crew
As America mourns the loss of space shuttle Columbia, BBC News Online looks at the careers of the crew feared dead in the crash.